You may be paying more for part time care. I have had the hardest time trying to find someone that will only take my son part time. We now pay a daily rate of $38/day and he goes three days.
Most likely she has set rates for each parent and some parents might be paying the same rate as you.
Consider what your child is doing with her, arts/crafts, eating 2 meals and a snack, do they go on field trips, does she have a helper/aid, pre-school circ, etc. when I thought about this, it helped me realize just what I was paying for. I paid more at a different daycare for my son to just have free play all day, no arts/crafts or pre-school circ., now he will get all of it.
You could ask the others or even the provider but I doubt anyone will tell you what they pay unless you have a close connection with them. You could talk with your provider and ask her if you could work a payment plan that works with your budget, she may be flexible about it, and may not want to potentially lose a child over cost. Good luck!