I pay my after school nanny $25/day for 2 hours of afternoon child care. I pay her $20 if she comes in the morning to get younger DD off to school (~1.25 hours). I pay her $12 an hour for other intermittent sitting. I pay a high school sitter $10 an hour.
I have to ask, do you really want to do this? What happens if one of your own children gets sick, needs an appointment, wants to do a class, has a birthday party, etc. What if you want to leave early one Friday afternoon to get out of town for the weekend. What if you are sick? What if she has to work late one day? What if you want to do something on one of those days off?
This is a huge commitment to make to her. If it were me, I would offer to do back up child care for her. One of my neighbors did that for me today (DH is out of town, sitter doesn't work on Tuesdays, and I had a mandatory meeting) and it was a huge relief to know she was there for me.
But I would strongly encourage your friend to find either a regular sitter or after school care.
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)