I can give you some input though on higher calorie/nutrition needs though just from my experience.
When I was a child, from the time I was about six years old I can clearly recall eating just as much as an adult physically active man would. I remember it so well, because my whole family thought it was amazing as to how much food I could put away! It was the kind of thing where if we went to a restaurant, and I'd order a huge meal, the waiter or waitress would say "Oh no, honey, you couldn't eat all that," and my grandmother would say, "Oh yes, she can!" and I believe we actually had a free meal a few times because the waiter/waitress would bet I couldn't. I have a normal appetite now for an adult female, however I have noticed that I have to eat something roughly every two hours or else I tend to get dizzy, and I'm not hypoglycemic or anemic.
I've also noticed that if I do not keep my protein intake rather high (at least double the recommended daily amount) my skin gets worse. My dermatologist thinks that's because of how much protein my body is processing as it's shedding skin constantly.
The only thing I can think of is that maybe if you give her stuff that tastes sweet to her, like fruit, it might be a good way to start her off? I would think that taste and texture would be a very novel thing to her, so also maybe make a game of tasting things with different textures, and a game of maybe thinking of what color a certain taste would be? I'm guessing that making it fun for her would be a good approach.
From a nutritional perspective, you've got a fantastic opportunity with her diet as she's probably never had junk food, and there's so many studies showing how bad sugar is for people (added sugar). Maybe a good think in all this is you can raise a person with little to no interest in junk food... just a thought.
You might want to contact F.I.R.S.T. and see if they have the names of some other parents whose children have been on feeding tubes that would be willing to chat with you. F.I.R.S.T. does maintain quite a big list of folks willing to offer support. That list is typically organized geographically, but I'm sure they could make sure you get in contact with someone who's dealt with the same issue, even if that family isn't near you geographically.
Also, perhaps you could contact your local hospitals and see if they could put you in touch with parents whose children have been raised with feeding tubes?
I am female, and was born in 1972 with Lamellar Ichthyosis.