I have never heard of a "Benign" breast "Cancer". If she has cancer then it could not be benign.
Please ask your girlfriend,if she so desires, to post in this Forum herself with more detailed information concerning her situation and we will certainly try to help her the best way we can.
With the information you have provided here,we cannot figure out what is really going on with your friend.
One additional suggestion: the source from which your girlfriend would best seek more information about her diagnosis would be whoever "they" are ( her doctor, presumably?) that told her that she has a very rare type of breast cancer. "They" should be able to provide her with a citation for a medical/scientific journal article in which "the only known 4 cases, only in women in Italy," were reported.
In regard to your other question, there are many different forms of reconstruction available for women who have had mastectomies, and one does indeed involve using fat cells from other parts of the body (abdomen, thighs, buttocks, etc.).
Best wishes to both you and your girlfriend,