Paralyzed friend.. help?

So I've known this person since I was about 8. I'm now 20. I saw her about 4 years ago and she was fine. She always had problems with her kidneys growing up. Now I keep in touch with her on Facebook and I NEVER noticed that she was sitting in a wheelchair. I don't want to be rude and ask her what happen. Her cheeks are extremely chubby. I was wondering what could of caused this. I would like any ideas without any rudeness please. I really don't want to ask her. Thanks!