I used to work with MS patients, and I have family members with MS. I have my own problems with heat and fatigue, so I can relate
My guess, if she has CP-MS, is that she will not be riding very many of the thrill rides, and that fatigue will be a big factor in addition to the heat. So, a few suggestions. Make sure you are staying in a resort in which there will be places to just sit and be happy, and not be stuck in a room that is too small, or has no features she will enjoy. If she wants to go to the pool, perhaps one of the resorts with pool wheelchair access would be best. Cooling off in the pool would be good, and therapeutic as well. Plan *her* day around shows, pavilions, restaurants and resort time... and make sure that the rest of your party gets to schedule in the things that they want to do at their own pace, as well.
Take an umbrella for instant shade, and use it!!! Never stop the wheelchair in the sun, never, make it a firm rule, drill it into everyone. Take a Misty-Mate sprayer, one with a wide-mouth and pump, and fill it with ice and water, and use it. Wear wide brim hats and light colored clothes. Put sunscreen on all exposed surfaces, especially laps of seated persons - they get fried. Cover the wheelchair when not in use so the surfaces do not get hot.
If she overheats, you can take her to the First Aid Station where she can rest and cool down. That is also a good place to take care of going to the bathroom and hygeine needs, since the regular handicap bathrooms are not always appropriate for people who need companion assistance. There are some family and companion bathrooms in the parks, but in the First Aid station she can lie down if she needs to.
I am sure people will think of more tips for you. Be sure to look at the old FAQ (it is now out of date but still contains good iinformation) and ask questions!
