If those girls are as good as you say they are, they will have no problem catching up three days when they get back from camp.

For the future, make sure you have in your band handbook what *specific* circumstances will be excusable absences--eliminate all possible grey areas--and how far ahead they have to give notice (this is to give you enough time to make any adjustments to the band setup...I ask for two weeks if at all possible, emergencies do happen). That will keep others from trying to find ways to get out of rehearsals.

For example, a couple of my beginners spoke to me prior to spring break that they might not make it to the Spring Concert in May. Legitimate reason for the absence, and they will be missed...but they took it upon themselves to let me know that there might be an issue two months ahead of time.