My sister keeps getting small brown spots on her face. new ones keep coming up and they look like birthmarks. what are these spots?

Brown Spots on Face: Brown spots that appear on the face can are the result of hyperpigmentation. These brown spots or patches are caused by the occurrence of too much melanin in one area of the skin. Hyperpigmentation occurs because of one of three causes in most cases. It is either the result of melasma, age spots caused by the sun or an inflammatory injury to the skin such as acne or rashes.

Melasma: Assuming that's what it might be. Do consult a dermatologist. It is cosmetically significant, but need to confirm diagnosis.