1) Buses, have windows? That can be put down half way?
2) Sunscreen. Put it on her beforehand.
3) a hat
4) bottled water. I am SURE they are allowing kids to bring bottled water???
5) Per the age of the kids and the length of the field trip and that it is hot... ASK THE camp Leaders... IF the children, will be "allowed" to have breaks, and will they be directed to go in the shade???? To M., this is a must. There needs to be breaks and/or times that they are allowed to go in the shade etc. and to rest, at least for lunch break. And so that, the kids do NOT get, over heated or dehydrated...
6) ASK the Leaders of the camp, how they handle the day, the sun, the length of the activities, and per the age of the kids? Ask, them. Beforehand.
Then you will not have to wonder.
It is COMMON for parents to ask these things.
7) ALSO tell your daughter to speak up... if/when she is tired, or too hot, or needs a drink of water, and if/when she has to use the bathroom.
AND being the heat is SO high... yes, you may opt to keep her home.
Even adults, can suffer under these conditions.
And especially if someone has health issues.