I think $100 is very generous and would be a fair price to pay for your peace of mind
I once dogsat for these people that had FOUR dogs---one Pomerianian, one Chihuahua (in HEAT!!!), a Lab and a Pit (both unneutered boys, ugh!!!) They only paid me $80/day, and boy was that gig a major pain in the butt. The next time they went out of town, they wanted me to do it for HALF that, and I said thanks but no thanks. The Lab ended up severely biting the neighbor when she came to feed them and it ended up costing them thousands, so they didn't save any money, and the neighbors were feuding after that.
Anyway, she sounds perfect
!