USF ointment from Standard Process works AMAZING for skin issues, especially for allergy issues and open sores. Also, I would use pure oils, like grapeseed oil, rather than creams with all full of waxes (parabens) and phenoxyethanols. This is to help with healing the skin, while you can help her heal the inside, which is where this is coming from.
Allergy meds may help the symptoms, but that's not the reason she has it. She doesn't have a deficiency of Zyrtec. In my experience ALL skin issues is the liver trying to dump and so, since the body is not processing things properly it gets pushed out of the skin. Allergy meds will only drive it deeper.
Since a vitamin C COMPLEX with includes an equal amount of bioflavinoids to vitamin C, possibly with rose hips as well, is a natural anti-histamine and can GENTLY clean out the liver, not like milk thistle or dandelion, which will be too harsh for some 6 year old's livers. I use CBR (vitman C, Bioflavinoids, Rutin) from TheraTech. A large bottle of 250 runs about $25. You might consider giving her 2000mg of a vitamin C complex per day....so 500mg tablet 4x/day. Vitamin C is water soluble, so if you give more than the body needs at that moment, it will dump, so splitting it up is important. LOTS of water, so the liver gets cleaned out through the intestines, rather than forcing it through the skin, which might temoprarily increase symptoms. Stick with this for 3-4 weeks and see. I'll bet anything this will work. (PS, you can crush it up, if she can't swallow vitamins, and mix this in something for her.)