Moles, or nevi which is the technical medical term, are collections of pigmented cells, or melanocytes, that live under the skin. Moles are normal in all people, but they do sometimes carry a risk of transforming into melanoma, which is a serious form of skin cancer. Things that heighten the risk that a mole is becoming cancerous are as follows: if the mole is larger than 6 mm in diameter; if the mole is elevated; if the mole has irregular margins or is spreading; or if the mole has multiple colors inside of it. Based on these criteria, I would be worried that the mole your daughter has on her back is spreading. This requires evaluation as soon as possible by her primary care doctor
to evaluate for the potential for melanoma. After a physical examination, if your doctor has some suspicion that the mole may be dangerous, they will want to remove the mole for biopsy
to determine what is going on and to determine if further treatment will be needed. In the meantime, your daughter should protect her skin, avoiding tanning, and use sunscreen lotion whenever she is out in the sun.