Thanks @Nikkei_Simmer! That's what I did. The "stuck" spot on this house seems to be to the left of the gate in front of the mailbox. After I reset the Sim, she was invited over and promptly married into the family. The next day, she was forced to go to her graduation (she had just become a young adult the day before I moved her in). So the entire family hopped in the car and went to the graduation. When they came back, she and her new husband got stuck in that same spot. I reset the entire household first and they were still stuck. So then I reset her and her new husband and all seems well after playing them for three Sim days. Hopefully that won't mess up my game.