2 Year Old, Rash On Heels, Spreading, Itchy. Advise?

My 2 year old has a rash on both heels. It seems to be spreading across the bottom of her feet. It doesn't look like hand-foot-mouth (she has had it once before @ 8 mo.), her mouth and hands are clear. It looks similar to the eczema rash she gets on her cheeks every once in a while but a darker purplish color. She itches at it if her socks are off, otherwise it doesn't seem to bother her. I also thought it could be athletes foot but it isn't between her toes at all. Could it be the sandbox at daycare even though she always wears shoes? We also went wading in the river a couple of weeks ago.