Always tricky, dealing with friends!!
If you feel like you can salvage it, then I would offer the care until a) she finds another provider or b) you fill the spot. Make sure you go into it with the idea that it's just extra money, and no hard feelings if she pulls with no notice. And make sure that you are EXTRA clear that if you fill that spot, you will need to give her notice. It might be easiest to put your pride in your pocket and say "Hey, I feel like you are a little upset at me, but this is my income, and I need to know that a certain amount is coming in. I wish I could help you more, but if it means not knowing what I will be paid and when, I just can't. I hope you understand." You would think that she would!!!