"Strand" her for two weeks, and I bet she finds someone to live with faster than you think. She probably already has someone on deck right now. If not, take her back. Then come back to this topic and call me a liar.She didn't care what she did to you, so you don't need to care what you do to her. She wouldn't have even told you if you hadn't caught her in the first place.

Remember, that "one bad decision" just happens to be the only one you know about. If she is doing this after only nine months in, good luck spending the rest of your life with her.