Is it the money or the commute? If it is solely how much you are paying her, I'd let her know that you appreciate her, and that after reviewing your finances you're having a hard time making ends meet. She may surprise you and offer less tuition depending on how much less you need it to be. As a provider, knowing how difficult times are right now for people, also knowing that it's not always easy to find kids and good families, also knowing that it's an effort to bring new kids into care and not easy for them to always move from care, I would probably offer this if someone came to me and was honest about it.
On the other hand, if the price is too high, you're not really invested in having your child stay there and the commute is more desirable, you can just tell her that you have no complaints and you're terribly sorry that you just can't afford care right now. You don't need to necessarily tell her you found someone closer that is cheaper, unless you're concerned that the daycares are networked and she'd hear about it through the grapevine.
Sometimes giving less information is ok.
Good luck.... what a bummer.