C.F.
I think it really depends on the number of days you will actually need her. Plants only will need to be watered once, right? Is she dumping out the litter and replacing with new or just keeping it clean? If she is doing the plants once, mail and food/water daily and just keeping the litter maintained and not dumping it out at all, I would personally pay the following:
2 days: $10
5 days: $20
full 7 day week $25