You need to hire a real estate attorney to review all of the documents and understand all of the agreements between you and her. It is possible she owes you the money. It is also possible she does not. Only a good real estate attorney will be able to tell you what your chances are of recovering.
One red flag I see is that she lost the home to foreclosure, and she did not make any of the payments, suggesting she does not have any money. If that is the case you could get a paper that says you have a right to money, and no way to collect on it. That will run most contingency attorneys off, meaning you will likely have to pay by the hour to get the result you want. If she has ready assets to collect against, then there will be a different story.
You really need to have an attorney look at this. There are several issues that could drastically change the outcome that needs to be considered before spending time and money on this.
Good luck to you.
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You could have stopped it in multiple ways. I think you could have made the payments. You could have forced a sale. You could have filed a Lis Pendens. You are likely going to have trouble collecting this money from someone who could not even make monthly payments on the mortgage. I think you are wasting your time here...
I believe that this is a question best answered in person by a lawyer who focuses on real estate law. Said lawyer needs the opportunity to review all documents and correspondence related to your situation and to visit with you in depth about any agreements (in writing and otherwise) that you may have. Good luck to you.