You're absolutely right, it's an internal issue manifesting outwardly. Treating the outward helps the itch but doesn't cure the original issue.
In Chinese and Aurvedic medicine they call skin rashes as evidence of too much heat in the body, usually in a major organ such as liver or large intestine.
Since you don't want her to do a full flush, DO have her take in 1 tablespoon of a good oil 3x a day along with P&B shakes, as many of those a day as she can handle.
Have her stop eating anything really spicy hot, black pepper, bananas, tropical fruits (apples only are great), fruit juice, soda, coffee, black tea, dairy, sugar, flour, wheat. Stop as many of these as possible, or cycle the cheats every-other day, for at least 2 weeks, preferably longer.
Eat beets 3x week or more, any way she likes - canned, fresh/boiled, juice. Eat healthy whole-grain hot cereal as much as possible. (Bob's Red Mill or Lundburg's Brown Rice)
Use Brown Rice Syrup, stevia, honey or even saccharin or xybilotol (sp?) as sweeteners. (Saccharan really isn't that bad, not as bad as nutra-sweet, which is really bad.)
Eat this every day:
Cleansing salad 1:
equal parts olive oil (or flax seed) and apple cider vinegar
chopped raw garlic
chopped raw onion (white or yellow)
bitter greens chopped into bite-size bits or smaller
anythign else you wish to add
Cleansing salad 2:
1 cup carrot pulp or grated
1 tablespoon olive oil
1 tablespoon lemon juice
raisens and anything else for flavor.