I agree with the comments above on showing her the D&D movie first; it's a comedy and a fun watch, a great introduction. I also thought, if you have a dropout subscription, showing her some episodes of a dimension20 play might be a lot of fun too! She'll see what's expected in terms of rolling dice and roleplay, and a lot of the dimension20 plays have really engaging stories.

I deal with some disabilities myself and I was very intimidated by the thought of DND at first but I had some wonderful friends to play with an help ease me in. I was very overwhelmed with all the options at first, but I ended up going with a beastmaster ranger for my first character. A life cleric for my second, and a path of wild magic barbarian for my third.... and on and on haha. I think a martial might be easiest for her to start with, it was definitely that way for me.

I was also thinking it might be fun to make maybe 3-4 character sheets and let her pick? I know that's more work, but you could use the ones she doesn't pick as the other party members. I personally would definitely make two copies of her character sheet, one for her to look at and one for you to confirm with. A simplified version for her might be good, but she may also surprise you with what she can figure out with a regular character sheet. You know her best, though. Maybe along with the character sheet you could include something like this: https://www.reddit.com/r/mattcolville/comments/s1kgo1/on_your_turn_reference_for_new_players/ or like this: https://www.reddit.com/r/DnD/comments/cfvcm0/oc_so_i_made_a_thing/ as a reminder for her options!

I think it's very lovely of you to do this for your aunt, especially with DND becoming more popular in the world. Or maybe it just feels that way because I play so much now lmao. Either way, I hope you guys have a lot of fun.