I think I must be related to you. :-)
My mother and her family are from Orkney and we all have icthyosis except for one of my brothers (and I'm not convinced he doesn't have it, he has dry skin, terrible eczema and asthma).
I never had a proper diagnosis (just "Ichthyosis"), but I believe it's the EHK variety. Hands and feet.
Anyway we have the thick skin on the hands and feet and I have a few extra patches of dry skin where you would get writing callouses.
I've never found any of the moisturizers to work at all. Occlusion (putting the hands and feet in plastic bags, tied at the wrist and ankles) didn't work for me either.
If she does go down the moisturizer route, I suggest she moisturize her whole body even though it is just the hands and feet she has the problem with. If not, the moisture she just added will migrate to drier parts of her body through the skin and she's back to dry hands very quickly. If the whole body is moisturized it tends to stay moisturized. I doubt moisturizing will help her remove much of the skin anyway, and walking around with very wet hands is no better than having very dry hands.
What *did* work for me was getting a big rock from the beach and using that rock as the sponge I scrub my hands with after visiting the bathroom. The difference has been amazing.
Let me elaborate...
Sandstone works best, smooth rock like granite or marble is useless. Pumice stone is close to useless, it's a lot smoother than it looks and the holes in it will collect skin and become nasty very quickly.
With all the cracks on her hands, there is a lot of surface area to lose moisture from. It's critical that she reduces the surface area.
I use nail clippers to take off as much of the skin as I can, and to remove any of the painful "edge bits", then I just start scrubbing with the rock under running water.
Doing it under running water is pretty crucial, she needs the water to wash away the skin she's just broken off so the rock can touch the remaining stuff. It does work without the water but it is nowhere near as effective.
I personally prefer to use hot water to wash my hands, then switch to icy, icy, freezing water for the final smoothing phase. It reduces the swellings under the thick skin and gives the finger joints a break. It sounds unpleasant but the cold water kills the pain and reduces swelling while smoothing.
One good thing is that if she can smooth her hands very well and gets it under control, it becomes easy to maintain. In the beginning it's an epic struggle to get the hands looking "normal" but afterwards, just a few quick rubs of the rock after each bathroom visit and her hands will look totally normal except they will be a slightly different colour. Her hands could even be smoother than normal, as smooth as glass with no cracks is definitely possible.
A few other things I've learned along the way:
The dryness starts at the fingernails, then dries the fingers and then gets to the palms. Trim the fingernails and toenails religiously (again with the reducing of the surface area).
It might be best to leave the feet alone. Filing with the rock is unlikely to work because of the thickness of the skin (Before I started taking care of it, the skin on my heels could easily be an inch thick).
It's possible to slice off the skin with a large kitchen knife, but that obviously has it's dangers. If she does go for that, I suggest a very slow, sawing movement with a tense arm. It would be so easy to have the knife jerk into your leg. Apart from the danger, it doesn't give good results, the skin on the sole always ends up uneven, and in my case makes it even more painful to walk than normal.
If she does decide to use a knife on her feet, bigger is better. Most importantly she needs to be able to keep a grip on it while contorting her legs to get at the bit that needs cutting. After half an hour of doing that her hands will be slippery with sweat. A piddly little knife will slip and go flying (I know from bitter experience).
The rock should be quit flat. You need the flatness for the palms and then you need the thinner edges to get into the creases of the hands. The rock should be quite big, basically the same size as the hand. A rock twice as big will do the job twice as fast because there is more contact between the hand and rock per stroke.
I've found it's the difference in colour between the creases and the flat parts of the hand that people notice visually. Smoothing the flats but keeping the creases can actually make the problem stand out even more. If you eliminate the creases then people just don't notice anymore, even if the hands are red or yellowish in colour. I used to get asked about my hands every single day but since I found the rock 9 years ago I have not been asked about it once, not once :-)
People would also notice by the feeling of the roughness when shaking hands. This is upsetting for them when they realise they are grasping a surprise diseased hand and obviously upsetting for us. After smoothing they won't notice. In fact I've been complimented on the softness and smoothness of my skin when shaking hands (which was kind of a weird thing to say, now that I think about it).
(Since getting "The Rock" technique down, I've "worn out" two big hefty rocks from the beach. They're smooth as marble now. which I thought was pretty neat.
The middle joints of my fingers on my right hand have the dry skin after they were rubbed red raw while learning to write at infant school. I'm sure she's well past that stage but still, avoid any long term rubbing, especially on the back of the hands and fingers. Learn to touch type and throw the pencils away.
Keep nail clippers handy in every room. The little tiny sharp bits at the edges of the hand are very painful and worse, they add to the surface area of the hand and so hugely accelerate drying.
Smoothing also softens. It breaks the rigid connections between the hard skin cells making the skin pliant and bendy.
If you ever watch someone preparing animal hide to be used in clothes you'll see they scrape it back and forth with a bit of wood. It's the same technique.
My wife loves how smooth and soft my hands are which is a far cry from my high school days let-me-tell-you!
Keeping It Up
Any regime is going to be a huge pain to follow. The trick I used was to make it part of another routine. I have to wash my hands after using the bathroom anyway so why not smooth my hands at the same time? In fact lets swap my sponge for my hand smoothing rock, now I have *no choice* but to smooth my hands. It's practically automatic.
It becomes easy to maintain once you are "over the hump" of the initial smoothing.
If you skip a day then your hands will be right back to square one. A crack forms, which accelerates the drying, causing more cracks to form, which speeds up the process even more and so it goes on.
I do about 50 strokes of the rock per hand per visit to the bathroom. So 100 per visit. I go to the bathroom about 10 times per day (yeah I drink way too much coffee).
It sounds like a lot, but it's really not much more than a normal hand washing routine, and it does feel therapuetic and relaxing to do. I think of it like a hand massage under magical pain relieving water.
I have nail clippers within arms reach in every room, and I use them perhaps 5 times a day for "touch up jobs".
Be methodical. It's surprisngly easy to miss smoothing part of your hand again and again. If you just can't get at it with the rock, then snip it with the nail clippers. Every square inch of the hand has to receive some kind of attention, or else it's a waste of time. A rough spot will draw all the moisture from the smooth areas you just spent ages on and will undo all your hard work very quickly.
If her feet hurt after walking (mine are agony almost every time), as soon as she gets in the house, she can run the cold tap in the bath for a minute until there is about an inch of icy water in the bath and then she can just stand in it. For me it relieves the pain instantly where painkillers fail miserably. Just 60 seconds standing there is enough to completely cure the pain for the rest of the day.
See if there is any way aspects of her condition can be framed as a benifit. For example she can probably touch hot things.
I work with computers and I can handle red-hot chips without being burned. I can touch low-voltage electronics without being electrocuted (don't try this at home folks ;-)
I can peel potatoes faster than the eye can see and with stunning accuracy because I know I won't cut the palm of my hand or my fingers.
I can use my hand as a makeshift pin cushion when sowing.
I can stub out a cigarette on the palm of my hand and look like a real nutter (should the situation require it ;-)
Too many examples to list. I use my Icthyosis super powers at least once a day.
The only thing she will probably never be able to do is to snap her fingers. I still try once a year but it hasn't happened yet *sigh*.
Oh yeah did I mention "surface area" in my post? :-)
Rocks are the best things ever invented. They're just so versatile.