Time is tight, but I would look (quickly) at some
YouTube videos to see ride vehicles in action.
BigFatPanda is good - Pammie might be better in this case, as she has great videos that often show the ride vehicles, seats, loading/unloading.
Your biggest hurdle is that bent leg cast. As the mother of a kid who was in bilateral casts from her hips to her toes for a long time, you will have to make sure that the cast is properly supported when she is on a ride to help protect the leg inside so that it doesn't dangle which could lead to swelling and pain, and also that the backside (above the knee, on the back of the thigh) doesn't break down, either internally, externally or both. (much less likely with modern fiberglass casts, but still a possibility)
When renting a wheelchair, try to make sure it will have the ability to support the leg in a position that is comfortable for her. Adult wheelchairs may be too big - again, her leg will dangle uncomfortably, which could also lead to swelling, pain, pressure... all not conducive to healing properly.
If she is small enough, and you can support her properly, you may need to consider a special needs stroller just for this trip. You can get a "stroller as a wheelchair" tag at Guest Relations at the first park you visit.