Our best man (FI's brother)'s wife has been getting sort of mean regarding our wedding lately. She told someone they could bring their baby to our no-kids wedding (she knows it's no kids, she told us she told the cousin we'd make an exception, we still have no idea how to politely correct that), she showed me a picture of a white dress and asked if it'd be OK for her to wear it to our wedding, she RSVP'd to the bridal shower then didn't show up and never apologized, and she has complained about the wedding every time it comes up (sometimes she brings it up, and I'm starting to think it's just so she can air her complaints about it).
Just recently she told FI's mom that on the wedding day, the groom and best man were getting ready at the best man's house, and then the 3 of them were driving to the ceremony together. We have no idea where she got that, FI and his 5 groomsman are planning to meet elsewhere.
We think she has massive separation anxiety regarding her husband on the wedding day and is voicing it in jabs about the wedding. We think the best man might even follow the limo in his car to take pictures because his wife doesn't want to hang out with the family while we do that. When you tell her, you know everyone in the family, it'll be OK, you'll hang out with X, or Y, or Z, her response is, "Oh yeah, like I'm close with those people."
We also know there's some jealousy involved because our budget is bigger than theirs was - a lot of her comments are about how we have so much more money to spend on our wedding.
We try to brush it off, but FI isn't always super communicative with his family, so I'm worried this girl is going to give out a bunch of misinformation that will ultimately reflect poorly on us. Plus, the negative vibes are just stressful and uncalled for. Do we address this somehow? Or just keep correcting things when we can?