I have worked with licensed and un-licensed daycare providers, and since you aren't claiming it, you tend to pay less over the ones that would. That being said here's what I know..
Usually it's about $30 a day for one child. (give or take a few dollars based on age). So you paying $100 for weeks with 3 days is about right. (a bit on the HIGH end, but) Though with all those, I have always had snacks and lunch provided. She's really making out with you sending all that and giving equipment.
For the second one, you usually get $5 off a day, approx. So that would be $55 a day - $165 for three days. Again, that's with lunch and snacks and equipment being provided. I would think that if you wanted a CONSISTENT amount for her to get even in the summer, I would say $150 would be generous given she gets an extra day off in the summer.
Most sitter's ask that you guarantee a certain number of days.. so I can understand paying her the same in the summer, but then balance it out with an adequate amount for winter...?!
Just me.
Good luck, money talks are NEVER easy.