Hi.... I just read your query. It would have been helpful if you had mentioned your daughter's age . Nevertheless, painful lumps are not generally alarming. It is the painless lump which is a cause for worry because it may indicate a tumour. Your daughter probably has mastitis i.e some infection in the breast tissue which should improve with a course of antibiotics. She may take some anti-inflammatory drugs and do warm compress for pain relief.If the lump persists despite the treatment, it needs further investigation. Till then, you need not worry so much.