What Causes Lump In The Breast?

My daughter has her first child born almost 4 weeks ago. She has never been good at doing breast exams and can t remember the last time she ever had one by a doctor. Now because of breastfeeding she is aware of 2 tiny gravel feeling lumps which are more pronounced when her breasts are full, but can still find them when her breasts are softer. Her 6 week follow up is in a couple weeks. Should she take action sooner or call them in advance to ask for an ultrasound at that appointment? I don t believe she has ever had a mammogram although she is 31 and her maternal grandmother died from breast cancer.