How can I prepare myself to be a companion to a girl with severe autism?

Well, first off this is so sweet of u, and speaks volumes on your character. With that being said, this statement is contradicting. It's impossible to treat her like an adult if she functions on a 5 or 6 year old level. That may have been the others problems. ie, a 5yr old wants to run after a ball in the street, do u let them... The person in question wants to do the same, although she's an adult, do u do what's best for her well being, or because she's grown do u let her do what she plz??? Just food for thought.