Hi Gary,
Fantasmic is no longer performed every night so when it is held, its super crowded. To check the performance schedule during your trip, click
here to get to the monthly calendar. Select April from the drop-down list. Then click on a specific day for the schedule for Fantasmic.
Wheelchair accessible seats are located on the top of the theater. I've heard that there are some on the bottom row but I've never sat there if there are (I wouldn't want my son to get wet from the mist). Only 1 person in your party will be able to sit next to your daughter. Other members will be directed to companion seats near you (if available). I've sat with my son several times in the handicapped sections & the view was great. If possible, avoid sitting behind the large support poles that can block your view during some parts of the performance.
Reserved seats for the dinner package are to the far right of the theater. The section is reserved but the seats within the section are not. If the wheelchair accessible seats fill up in the reserved section, you could be directed to another section. If you elect to go with the dining package, I'd arrive earlier than they recommend. If it is within your budget & you're able to get reservations for the dinner package, you may want to consider it to reduce your wait time.
Cast Members are great at accommodating those in wheelchairs & have always escorted us to a seat but you have to wait in line with everyone else. Disney is an awesome place for those with special needs. Because of that reputation, there are a lot of Guests in wheelchairs & ECVs that visit. Make sure you get there super early if you don't go with or are unable to get a reservation for the dining package. Seating usually begins 90 minutes prior to show time for those without the dining package.