There is much in your story which does not quite hang together. Erythema multiforme does not, for instance, cover the face or whole body. Not does it typically leave "white spots."
More likely, it seems to me, is that your daughter had a flare of eczema. This can rpoduce round, scaly patches which leave hypopigmenation (undercoloration). This can last for months before evening out, but it does even out, and all by itself.
Selsun cannot damage the skin permanently. The white spots do not represent damage or the potential for sun damage.
I advise you to have your daughter consult a dermatologist, who can perhaps look at her skin under a Woods light (a hand-held ultraviolet diagnostic device) to detect the degree of under-pigmentation and thus advise you on the likelihood of repigmentation.
I bet your daughter will be as good as new. Check it out.
Best.
Dr. Rockoff