Contact an attorney.
The mortgage lender through the settlement company had a duty to verify the identity of the person signing the document. They would do that by having the document notarized. The notary public would have asked for federal or state issued photo identification.
The mortgage is of public record so you should be able to look at a copy and see which notary public witnessed the signature.
If you are still married, questions will arise about whether or not you allowed her to sign the mortgage or had personal knowledge of the transaction.
Those are starting points for piecing things together but you need an attorney to protect your real estate, so don't dilly dally. Good luck.