They do strap wheelchairs, yes. However, that does not make a wheelchair safe either. It's a combination of factors. Some wheelchairs simply will never be safe as soon as something happens. And even if one is 'safe', the whole safety purpose is totally down the drain if there isn't a proper seatbelt in there. For those using a powerchair the belts on the busses tend to be OK (although not for all powerchairs), but for ECV's, lower manual chairs and strollers, that wont be the case for most. Don't know if you've ever seen how high those belts are in the bus? Totally too high to safely strap any kid in a stroller down using the 3-way. One can opt for only the lapbelt, but that also would have the downside of it not being the true safe way.
I don't know your daugther and how 'easy' or 'difficult' she would be to manage in a regular seat, which of course would also influence overal safety. Only you can make the decision which out of the two is the safest option for her. I personally use disney transport all the time, no rental car will do that.
I will stay put in my powerchair, not in my manual. I know that I am less safe in the manual chair (never mind having a lapbelt or not) than I would be in a regular seat if there is a sudden break. For me personally it is safer to stay in the powerchair belted in. However, when using own transportation I do not stay put in the chair. Never mind it being crashtested and the van fitting all regulations, it still is recommended to transfer as long as one can due to safety reasons. It all comes down to making your own judgement of what is the safest option fitting her needs, your families needs and/or desires etc. There is no real black and white in this, but seeing how often safety is totally overlooked I just wanted to mention the whole thing.
About carrying the stroller, a lot of that can be prevented. I would opt for using the wheelchair line and when the driver pulls up to quickly explain things. If seen A LOT of drivers being totally OK with parents with strollers using the back entrance. Explain the need and I don't think most would have a problem with you using the ramp where need be. In that situation, you could get her on the bus in her stroller and transfer her to a seat next to you once on the bus.
One thing I noticed a couple of smart dads do; store the stroller underneath the 3seats-benches. Note to that is that they aren't on each type of bus and 2 of them could be stowed to tie down wheelchairs. However as long as the bench is used for seating space, it also is THE perfect spot to put a stroller beneath. Sit yourself down on a seat above it and you can control the stroller during the drive with one or if need be two legs. That parent now ends up with 2 free hands they can use to hold on to kid where need be.
Don't know exactly how high that space is, but it is more spacious than having to take the stroller on the bus 'standing'. Maybe it would even fit with the footrest still on there?
Look, if it is too much of a unclimable mountain, have them tie down the stroller. But I would personally take daughter out of her stroller and trust myself more to hold onto her if there is a sudden break than her being in there with none or only the strapping systems for 'walking' usage.
Bus after Spectromagic to CBR? Hmm, you sure know how to temp faith.
If you would try the bus, do it at a slow time like noon or something. This way, you wont feel so watched or need to rush to try things out. If she does have a meltdown or anything, oh well the bus will probably be empty anyway. (read; also less triggers)
I love CBR. One of the aspects I like about it, is there low number of accessible rooms and how people tend to hate it as soon as they have any mobility problem. Which to me means; relatively less other wheelchairs and strollers around and thus more chance of me not having to wait for another bus if there are already 2 wheelchairs/ecv's on there or people in front of me. But to be honest? Taking the bus back around closure time for a park, especially after Spectromagic, Illuminations, Wishes etc. ..... well, that is a bit crowded. Even during the very slow days of September, I never once was on a bus back at that time of day that did not have people standing on it. Most of the times I had people more or less trying to be IN my chair, so many were standing.
Not a situation that might be the greatest for your daugther, especially after spending time at a park and probably having used up energy and 'tolerancelevels'. But, I do not know her and could be VERY wrong.