If she has a wheelchair and it solves her mobility issues she may not qualify for a
DAS. Unless she has other reasons she can not wait in line.
Correct.
DAS is for people who can't wait in conventional lines. All lines are wheelchair accessible, so she would be able to use the wheelchair in the lines without using DAS. There is a thread about DAS in WDW near the top of this board. The first post in that thread is DAS FAQs.
Fastpass Plus would let you be able to use the less crowded entrance, but if it is very busy, the wheelchair spaces can sometimes fill up while the theater is not full. So, choose an earlier Fastpass Plus time rather than a later one. If all the wheelchair spaces for seating are filled, there are some wheelchair parking spots where guests who can get out of their wheelchair can park and then sit on the theater benches.
For Fantasmic, the wheelchair seating is the entire top row of seating in the theater. The top row has empty spaces wheelchairs or
ECVs can park. Some of those wheelchair spaces have a seat for one companion to sit right next to the wheelchair. The 2 rows right in front of that row are also for the guests traveling with the guest using a wheelchair to sit. Those 2 rows are also used for guests with disabilities who need to sit near the top of the theater.
So, you may sit with one person next to her and the other 2 directly in front of her or all three of you in front of her.
This picture shows the wheelchair spaces at the left side of the picture, with small companion benches next to them. The 2 rows with blue paint are the handicapped/family seating.
(There are also a few wheelchair spaces in the very front row - the set up is similar with wheelchair spaces in the front and the rest of your party sitting behind).
You will find a similar set up for all theaters - wheelchair spaces with space for at least one to sit next to the wheelchair and the rest if your group in the next row ahead.