This is a very hard situation. The first thing I would do is suggest to your listing agent that you put your home back on the market. How much money did she give you as a deposit (escrow money)? Hopefully it is at least 10% of the purchase price. I would suggest going after the buyer for her escrow money. She needs to sign a form to release it to you, but she should. If she does not, you can sue her for failure to perform.
If it isn't this person, someone else will buy your home. Do not worry.
What was the reason stated for backing out?
Did you get a big deposit?
Let your REALTOR or attorney figure out how to put Humpty Dumpty back together.
Best of success,
Annette Lawrence, Broker/Associate
Palm Harbor, FL