Donor IVF is very complex. You may want to consult with an attorney with familiarity with reproductive medicine, so that your agreement with the next donor is more clear and you are protected. Some donors are found through the actual program where you are having IVF. In other instances, they are found through donor agencies. If the donor is known to you, then perhaps you can negotiate an arrangement between you and the donor that will protect you from this sort of financial vulnerability. If the donor is anonymous, then you need to understand the arrangements with the agency or program working with the donor.
I am really sorry to hear about this. This is very unusual, and more of a legal issue than a medical one, hence the advice to seek a legal opinion. Two well know reproductive lawyers in the USA are Melissa Brisman and Susan Crockin.
No, it doesn't seem fair, but it is her right.
Think about adoptive parents who go right up to the time of the birth, often paying for everything during the birth mothers pregnancy...and then she changes her mind and keeps that baby. That seems very unfair, but of course it is her right, too.
I hope it works out for you the next go-round. Good luck.
Yes, it is her right..but she is playing with your emotions. Some people don't know what we go through to conceive. It is not as easy as many think (birds & bees). I hope the next donor is compassionate and continues.