Grandparents and boundaries

Hey mama’s, I’ve got a question on how to handle grandparents who won’t respect your wishes when it comes to your kids. Here’s an example: a few weeks ago I got into a heated discussion with my mother about putting my kids in their carseats with winter coats on. Its dangerous bcs the straps don’t fit right. She doesn’t think it matters because “she did it when we were kids”. I say that doesn’t matter and I’m their mom so she should respect my wishes and keep them safe. Fast forward to this past weekend, she took them again, and when she brought them home, they were, once again, in the carseat with coats on. I was livid. The drive from her house to mine is an hour, and its mostly highway. I just don’t know how to handle this. She always refuses to follow my wishes, and tries to micromanage the way I parent. Its infuriating. The carseat/coat issue is just one example of many. If you’ve made it this far, thanks for reading.
Sincerely, a frustrated momma bear