while she could be more shy than most girls, i would just approach her like any other girl (for fvcks sake don't sneak up on her). People with disabilities do not like to be treated differently than anyone else. Although you will definately need to take this a little slow, and she will have to trust you before she will let you take her anywhere im sure (since she won't know where you are driving her, etc). Try just hanging out with her in a casual atmosphere not a date at first cuz its definately going to be hard to get her to trust you. You could definately kino this girl and im sure she will respond well to it since it will help her know where you are, etc. Probably not going to be a good movie date (wich you shouldn't do anyways) or anything like mini golf (wich I also think is gay) but im sure you can score a coffee date with her. Your verbal game is going to have to be pretty tight, cuz your looks aren't going to score you any points here.
One last thing, don't treat her like shes a charity case to be dating or anything, pimp her like any other girl.