Visit from the mom in law

My mother-in-law is coming to spend the night tonight. She lives about an hour from us. Not a big deal in the south. In fact, I drive an hour to work each way. I love her, but I don't understand why my husband wanted her to spend the night so badly and why she felt the need to accept. Originally, she was going to stay a night at our place on her way to visit my sis-in-law - 4 hours north of us. I was ok with that since it would save her driving time. Then she was like, "I don't know when that's going to happen, so I'll just come see yall." Jeebus.