Welcome to health care magic!
After reading your question it is evident that your sister has three mass in her breasts but all appear bening according to the radiology report.
"Bening" means they are non-malignant/ or non cancerous in nature. More over there are no visible, or palpable masses in any axillary region that again goes in favour of bening nature of the masses.
From my experience I can tell that it is a common condition, can be seen in young females also.
Had I been your treating doctor , I would also go for an FNAC (fine needle aspiration cytology) of the masses to be absolutely sure of the condition.
I would also like to say that sometimes these masses might hurt and they increase in size with time.
If your sister feels much concerned, she may go for small surgery to remove them, it can be done under local or general anaesthesia
Hope this answer helps you.
Please feel free to ask more regarding this.
Dr. Manisha Gopal