1. As you said, there is a mortgage contingency provision in the contract, but I bet there is also a good faith provision thereafter. This means that the buyer has to be in good faith trying to obtain the mortgage at a prevail rate. So what is prevailing rate? It is anybody's guess, but usually anything below 10% is.
2. I believe there could be also a provision in the contract that allows the escrower, usually your attorney, to release the deposit earlier. If indeed there is, just take a money and wait for her to sue you to get it back. Remember in civil case it is almost always beneficial to be the defendant. Then you can decide how to negotiate it with her and whether you want to retain a lawyer to help you.
2. I believe there could be also a provision in the contract that allows the escrower, usually your attorney, to release the deposit earlier. If indeed there is, just take a money and wait for her to sue you to get it back. Remember in civil case it is almost always beneficial to be the defendant. Then you can decide how to negotiate it with her and whether you want to retain a lawyer to help you.