I think that's sweet of your sister to offer. Doyou have some reservations about letting her for some reason? Does she have other animals there? Other family members besides herself?
I understand your feeling...it's like we don't feel anyone can care for our babies as we do. Maybe you can let her keep him for a couple days prior to Monday to see how it goes.
I hope it works out for you so you don't have to worry...you have enough to concentrate on. I wish you the best on your surgery and pray for a speedy and full recovery..