bad diaper rash

my daughter goes to day care and she had diarrhea the past days due to milk change. It went away and now it's back! The teacher didn't inform me and I leave diaper cream in her school bag. I'm so pissed off and it's so bad that my daughter won't even sit or sleep. It's to the point it will scab up. Can I take her to the er? She won't allow me to put triple paste on