Husband's mom

My husband's mom gets jealous of people real easily. My husband and I are both 30, and have a house under contract. We are supposed to close on it Aug 30. His mom, who is in her 50s, struggles financially and lives in a very small rental. She can't afford to rent/own anything over $500 or so a month. Our mortgage is going to be $865, plus utilities of course. It's a nice house--built in 2008, 3 bed 2 bath on just under 2 acres of land. We haven't rubbed it in at all to anyone in his family. In fact, we just said we were buying a house and that's been pretty much it. They asked for specs, so we told them. Now his mom is acting standoffish and really weird. I hate it for my husband, but at the same time it's not our fault that we're in the position to buy a house. He'll be her first child to be a home owner. Help???