A.
I would consider the day hours at a reasonable hourly rate since she really will be quite busy with a 3 year old. (For example, 12 hrs of daytime at $7/hr) For nighttime, I think an overnight fee for her inconvenience (50-100 each night) is appropriate. Leaving money for take-out and such is also a nice touch. This may be higher than both of you were thinking since she is not doing it for the money per se, but something fair along these lines would be appropriate in my opinion. This also at least gives you a starting point of what to consider. Have a great time!