sounds like she shas a problem mainly where she sweats, and her clothes rub? is it her stomach and back just above or below the waistband of her pants? that's where my dd always got it.....and then her arms and legs. sounds like you are being careful what you wash her with, and weather changes are terrible for exzema.
try something: go to family dollar and get a stick of cocoa butter. less than 2 bucks. cut it in pieces, put it in a glass bowl and melt it in the microwave. melt it no longer than one minute at a time. the bowl will get hot, so be careful. add equal part olive oil (if it's an ounce of cocoa butter, add an ounce of olive oil. a shot glass full) beat it with a mixer until it gets cloudy, and pour it in something else. something clean, with a lid. try that on her itchy spots after bathtime while her skin is still damp.