I have a bit more time, so here's some examples of what I mean when I say that
DAS causes more walking. First, I planned animal kingdom to start in Pandora: get a DAS return time for navi river ride, use fastpasses for the flight of passage, look around the shops and explore Pandora, then return to use DAS for navi river. Then head over to Africa, do festival of lion king then use fastpass for the safari. But when we got the return time for the river ride it was almost 3 hours, and I just hadn't planned on it being that long. so after we did everything in Pandora we still had over an hour until our return time. so we went to Africa and did festival of lion king a bit sooner than planned. but that made us early for our safari fast passes. we did the rest of what we wanted in Africa, and it was still too soon for the safari but it was time to do the navi river. so back over to Pandora, then when that was done back over to Africa for the safari. Another example, in Epcot her favorite ride is mission space, so that's what I got the fastpass for. I planned to get a DAS return time for test track, use fastpass for mission space, then she loves to play in the fountains over in that area so I figured that would use up a lot of time while we waited for test track, and if there was time left and the line wasn't too bad ride standby for mission space again. but the return time for test track was 110 minutes, again longer than I had planned. and the fountains were turned off, so there went that part of the plan. we did our fastpasses for mission space, then the standby was only 10 minutes (much shorter than I had anticipated), so that hardly used up any time at all. we went to the big mouse gears shop that's nearby and did some shopping, then got a snack, but we still had half an hour left until our return time. we could hang around doing nothing, do standby for test track, or move on to a different area of the park. we moved on, and by the time test track return time came up no one felt like walking back over. there were times when having the DAS was useful, but you really have to go in with a plan, and use it together with fastpass, to avoid the constant walking back and forth. and if anything goes wrong with the plan, whether a wait time is longer or shorter than you had anticipated, an attraction is down, or you have to skip something for medical reasons, it can completely throw off the plan and then you end up walking back and forth, crisscrossing the park. My daughter uses an adaptive stroller (she is 9, various medical problems but mentally is a perfectly normal 9 year old. there was a time she was embarrassed to be using a stroller, but she realizes she just can't have fun without it, and got over it), so I am the one who ends up doing the walking/pushing, but even so she sometimes tires out and isn't up for going back and forth between attractions. I can't imagine asking a child with mobility problems to do all that extra walking. If you feel that DAS will help your daughter then certainly ask for it, but I would plan on using either a stroller or a wheelchair too.