My mother-in-law always doesn't use the caseat

Just found out my mother-in-law took my toddler out for a quick errand and didn’t use the carseat. I’m honestly freaking out a little. I know accidents can happen in a split second, and I just can’t stop thinking about what could’ve gone wrong. I always stress how important the carseat is, but maybe I wasn’t clear enough? I feel guilty for not double-checking, but also upset that she didn’t think it was a big deal. Has anyone else dealt with this? How did you handle it? I want to keep my kid safe but also don’t want to overreact. #ParentingStruggles #CarseatSafety #MomLife #Parenting