It's speculation on my part. Perhaps a different social platform.
1. He knew they were away. Not a stretch that he knew where they were.
2. She avoided social media. But most people don't. And many people post things on social media with considering or recognizing risks. Publishing an obituary online tells endings in the universe which hours you won't be home, for instance.
3. Something upset MT, related to MM. He was at or in their house at the same time. Unless she had a premonition, which I doubt, something real upset her. I do not think she knew where he was but I think he found a way to make sure she knew that he knew where she was.
4. She may have left the game because she thought he was AT it. IMO if she believed her been to her house, I doubt she would have returned to it.
5. That MT was also upset at the same time he was taking obvious steps toward a home invasion and murder, IMO it wasn't enough for him to want get dead. Cat and mouse. He wanted her to know he was winning. So calculated, evil.
JMO