My 13 year old daughter says she has one large lump in each breast, that takes up almost each breast. It hurts when you apply pressure. What to do?

See doctor. The most common causes of lumps in a girl this age are a fluid filled cyst or a noncancerous mass called a fibroadenoma. I recommend you contact her family physician. They should send her for an ultrasound and evaluation by a breast specialist. If she needs surgical removal of the lumps, make sure it is a surgeon who will be concerned with the cosmetic outcome. It may require a plastic surgeon.
Breast Buds. At puberty, as the adult breast begins to develop in a young girl, it is not uncommon for tender lumps (breast buds) to develop. This is the normal onset of secondary breast development. This is called thelarche. It is important to understand these are normal, and are not to be excised. This will pass. Please contact your family physician and/or gynecologist for a detailed explanation.