I would say $150/week is good if she is supplying the meals. In my area at the bottom of NJ, the average is $25/day which includes snacks, but not meals. I missed how old this child is. Do you have others at home? Is she paying you cash? There are tax implications if paid by check and I think you have to decide if she takes care of paying taxes and SSI etc or if you have to claim as an independent contractor. Look into that. If it's all cash.....
If she is going to claim the money on her taxes, then you will have to also.