PLEASE go out for sports! I'm 20 years old and I have NEVER been able to try any type of sport. My mom was afraid that I would get hurt since my skin is fragile so I spent my time on the sidelines. It is not fun and I would still get hurt because you can't control everything. For me, my joints do hurt when I stretch but I'd think it would be worth it for all the joy you'll get.
Best of luck and I hope she changes her mind!!