Toxic Mother in law......

Our 3 month old goes to the Inlaws house during 2-3 days a week since both of us work during the day. MIL usually picks her up in the morning and then drops her off when we get home.

My wife got a call from her brother (who i trust) who just got off the phone with my MIL (who was in route with our daughter on the way home, 20-30 ish minute drive). He said he heard some concerning things, the main thing being her yelling racial slurs (the N word with a hard R) at other drivers and me being half black. I know my 3 month old can't understand words yet but obviously I'm not a fan of that. She's probably done this since my wife starting going back to work (this would be the 3rd week) we really can't police what she does when she's in the car. My wife says she'll talk to her about it but I know MIL won't change her ways and how she acts, I do feel bad for her kids since they've dealt with this their entire lives. I really don't want my MIL to continue to drive our daughter around while that language is being used, part of me wants to just start taking her to our office (we work together) more days now but maybe I'm over reacting.

Just wanted to vent and any comments/advice, i'm all ears.