What should my mother-in-law do if she is careless and doesn't like cleanliness?

Then don't let her take care of the children!

Or think like this: mother-in-law is better than nanny! The nanny may give your child sleeping pills!

My mother-in-law is older than you. It is impossible for her to change her personality and habits for you or your children, not impossible in general. So the relationship between mother-in-law and daughter-in-law is an eternal problem!