Maybe get her tested, just because Mikey came back neg to everything doesn't mean she will.
I know how you feel though Spencer had an out break around this time last year and the allergy doc tested him for all sorts (he is allergic to dairy, eggs and peanuts but flared up even though he hadn't been exposed to those) and nothing new came up on the tests, then about 3 months later it disappeared as quickly as it had appeared. Luckily his wasn't on his face, just his head and torso but still not nice.
The only thing I can suggest that seems to work is alpha Keri oil in the bath water and lemnis fatty cream and lemnis fatty cream with hydrocortisone (which I think you need a script for) oh and a probiotic couldn't hurt to try either, they do powdered ones that you can just mix in cereal or yoghurt without them noticing it.