3 year old skin rash on her arm. it becomes invisible during the day with a few visible pimples, but at night it becomes worse and red. please assist.

Hard to assess: Rashes are hard to assess when they are not seen or well described, but there are some basics you can think about. Things that are localized to a single area are more triggered by a local contact agent as a reaction. If diverse, they are more likely food or illness or general contact items (bath soaps, shampoo). If this doesn't help & it bothers her have it evaluated.