The spaying does take a while to recover from. She should be okay for the training class on the 25th, but I'd keep her quiet and minimize movement until them.
The last dog I had spayed opened her incision - she even slid out of the elizabethan collar
! Some of them just mess with it
.
She'll be okay. Just keep that collar on and know that she might be grumpy about it. In a few more days she'll be feeling better and soon enough you can take the collar off. My dogs don't get aggressive when they've worn elizabethan collars, but they definitely make it clear that they hate the collars and they mope around.