Hi, is the problem only on one side? Dies she have any painful lump there? Was there any trauma yo The site? Is there any discharge from breast? Is there any other sign of the girl growing older, like hair In pvt part or in armpit? Is your child overweight? If no,  I would suggest wait for 2-3 months and watch. For pain give plain paracetamol. Do not press the area very often to just check It might be that child is in growing phase, and girls do get such pain at times. Hope this Helps you.