A.M.
i understand you don't want her to feel bad, but this is a good life lesson. life isn't always what we'd call "fair" and sometimes someone gets to do something we don't get to do...no biggie. don't make a big tragedy out of it.
however, i do think it's a great opportunity to do some really special mom and me things with her. a "spa" day with mom would be SO fun, even if she only gets her fingernails painted. you're in a great place (i assume) for zoos, museums, etc...don't pack every single day chock full of distractions but plan one or two special things just for the two of you to do. the boys might get to go to camp, but she'll get mommy all to herself and that will be awesome for her. have fun!