What could this be? Rash help

Ma

When my 2.5 year old woke up from her nap this is what her belly looked like. I called the doctor and they said to put ointment on it. We gave her some children’s Benadryl as well but after 2 hours it’s only slightly lighter. She didn’t eat any new foods today but we did go berry picking. Could it have been from rubbing up against a certain plant or something?