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I am sorry to hear about this situation. I am going to assume that you and buyer have a contract that states (a) when she is supposed to pay and (b) how much, and that (c) once she finishes the payment, you will sign over the deed.
If so, then someone in your situation simply does not have to accept any amount of payment less than what was agreed upon in the contract. And if the contract does not allow early repayment, then she cannot do this, either.
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