FYI, you can get larger boxes of the one-time use cold packs online. I bought a box of 24 (for home) on
Amazon for under $20 a while ago. When I'm going out, I grab a couple to bring along with me. I have severe heat intolerance (not from MS) and it's saved me more than once from serious problems while out. I've twice been to WDW at almost the exact dates as you'll be there; one year it was fairly pleasant (low to mid 70s), but the other it was 80s & 90s and very humid (despite the fact that it hadn't rained for 3 weeks, which is unusual that time of year). For me that's enough to cause problems so I'd possibly go through most or all of a 24 count box in a 2 week trip. You might want to consider ordering a box of the cold packs online to be delivered to your resort. If you end up with extras, you can either bring them home or see if you can find someone to "pay it forward" and give them to. Anyone who wants the info on the specific ones I bought, feel free to PM me for a link
I know they're not as environmentally friendly as re-usabled cold packs, but I don't need to worry about finding a way to freeze, wet, or get ice from somewhere for the disposable cold packs.
The
DAS is for needs that relate to having problems waiting in line that do not deal with mobility or stamina (for those they recommend an
ECV or wheelchair). So most or all of her limitations may be mitigated with the ECV. If she has additional needs, what she needs to be able to explain to GS is what her needs are that prevent her from being able to wait. If you want more info, there's a sticky on DAS (make sure you look at the one for WDW, not DLR) at the top of the board and the first post has been kept up to date with all the information about the DAS and how it works. Most lines are mainstreamed so she'll be able to bring the ECV through. There are a few where an ECV can't go through the line, but a wheelchair can. For those she'll have the option to transfer to a wheelchair (they should have them at the ride for you to use) or walk through the regular line. For attractions where the regular line isn't accessible your party will either be directly sent to the accessible entrance (often the exit) or, if there are a lot of people waiting to board through the accessible entrance, given a "Wheelchair Return Card" with a time to return. These are completely separate from the DAS. It's unlikely to happen, but you can hold multiple wheelchair return cards at once. You have an hour window to return after the time on the return card. There's no way to know in advance if one of the rides with return cards is actually using them since it varies on how busy they are and she will have to be there to obtain the return time.
There really aren't many rides that have alternate entrances and most are in MK because it's the oldest park. There's a FAQ in the stickies on this board that has a list of the rides with alternate entrances (which are the ones where there's any chance of getting a return card). The only ride that does not have any accessible entrance is Tomorrowland Transit Authority (or whatever it's called these days); the line is an inclined moving walkway so even if they could stop it, it wouldn't work for access. Of the accessible rides with moving walkways, Peter Pan is the only one that can't be slowed or stopped; she'd need to be able to board PP in the same amount of time as anyone else. I have heard of guests being allowed to enter PP and watch to see if they can transfer in the time allowed (I'm probably the only person ever whose been to WDW more than once and not ever even tried to ride PP so I can't confirm and these days I doubt I could make the transfer safely) . Again, there's a list of which rides can be slowed/stopped in the FAQ. The only extra warning there is that some CMs don't always like to slow or stop the walkways. It's worth pressing, especially because the time of year you're going really isn't very busy.
I'd suggest considering a plan involving touring from rope drop until midday/early afternoon, taking a few hours to rest/relax back at the resort, and then returning in the evening (around dinner time) if you're all up for it. One of the reasons is that will avoid the hottest and sunniest times of day. Another way to avoid some of the heat is to alternate indoor and outdoor attractions. The majority of the exposure to heat/sun is going between attractions. If she's on any meds that increase photosensitivity, she should really make sure to wear sunscreen (at least SPF 15, but better if it's 30+) and try to go with long sleeves (even better to wear clothing with extra UV protection built in).
The other big reason to go back to the hotel in the middle of the day is so that she gets a chance to rest and recharge. She can also rest in First Aid if needed, but I don't find that as restful as an actual break lying down in my room. It's always easier to try to prevent fatigue than recover after it's gotten to be too much. The same thing regarding prevention is true for pain as well. The ECV will help with preventing both pain and fatigue from increasing, but more active prevention is the best. That could be the break, it could be talking to her doctor about an additional pain medication to bring (and actually use it when pain starts to get worse than normal, not wait until she can't stand it), or could be something else. She probably knows what works for her.
During the trip check in with her to see how she's doing, but don't insist she has to do something to mitigate symptoms (take a break when the rest of you aren't, take a med, etc.). She isn't going to want to be treated like she can't make her own decisions about her care. Sometimes well-intentioned relatives/friends get over zealous about protecting someone with a disability/chronic medical condition so that the person with the condition feels like they're being treated like they're a kid. All that does is make the person mad and less likely to be reasonable about taking care of problems appropriately. I'm not saying you do (or would have done) that to her, but it's such an easy trap to fall into without realizing that I wanted to mention it. Suggestions or reasons why it might be better for her to do/not do something are okay if she admits to or obviously has a problem. I'm sure she also hates to feel like she's slowing/limiting the people she's with. This can lead to not speaking up when problems do occur. That's one of the reasons building in that planned resort time in the afternoon for the entire party can be beneficial. She won't feel like she's left out or causing the family to alter plans because she got tired/started having extra pain. Plus, the time back at the resort can recharge everyone and/or give you a chance to see things there you wouldn't normally.
Finally, hydrate, hydrate, hydrate. It's worth asking her to ask her doctor if there are things that are better for her to use than others. In general water is the best for most people because anything else has something in it that reduces the effectiveness with hydration, but some medical conditions mean something else is better (or needed along with the water). Making sure she has access to food and eats relatively close to her normal schedule is also important.
Sorry for the overload of info. I have no idea if all of it will be useful, but I wanted to think of as much as I could. I hope you have a wonderful trip!