How do I tell my mom she needs to do better

My mom watches LO when we work. For the last 2 weeks LO has been on antibiotics for a ear infection and has had diarrhea from it. Last fri my LO came home and had a really bad diaper rash. It took all weekend to clear up and on Monday when I dropped her off I told my mom about the bad diaper rash and to make sure she changes her often and put diaper cream on with every changing. I picked her up and diaper rash was back. I have noticed from other times that she will come home and there will still be poop in her folds.Not a lot but still... I dont know how to confront my mom on this. I dont want her to feel like we're not grateful for the help or that I dont think that she is doing a good job but this bothers me. How do I confront her without it being negative?