12 year old daughter has small, white, flat round patches on her forhead. what can it be?

Tinea: A picture truly is worth 1000 words. In this situation without actually seeing the patches it can be hard to make a diagnosis but if your daughter has been the sun then the white patches may reflect the growth of the type of fungus that's called Tinea versicolor. This is not dangerous but can be annoying. The superficial fungus is like a window shade that blocks tanning . Chat with your healthcare provider to discuss therapies

Many possibilities: These could represent common fungus (tinea corporis), flat warts, a condition called pityriasis alba, as well as many other issues.Some benefit from treatment and some self heal. Because they are in a cosmetically sensitive area on a girl, I would have them evaluated by your doc to see if treatment is needed.