Hell no lol. I would seek her out and demand my money back and pay her only for what she worked for. Or take back something of equal value, sell it and give back only he weeks worth. No cops needed. I don't deal with cops. Ever.
But anyways, that's straight up breach of contract from the sounds of it. But I can also see your point in just letting it go. Sometimes it's best for sanity sake but it can leave a message for everyone else that people can walk over you and oh boy...
They will try.

Perhaps though, it serves as a good lesson also to never pay until the job is done and well.

Edit:

Just to clarify, I don't see that as revenge at all. Revenge is about making someone suffer because they wronged you. What I'm talking about is justice. Restoring what was agreed to. If someone is paid for three weeks of work and walks away after one, I don't see asking for the unused portion back as punishment. I see it as honoring the original agreement.

For me, forgiveness and justice aren't opposites. I can forgive someone without pretending nothing happened, and I can let go of resentment while still expecting people to be accountable for their actions.