You have evidently consulted some excellent medical practitioners regarding your Daughter's problem and their advice seems quite reasonable under the circumstances. Fibrocystic Breast Condition affects nearly one half of all women and often begins in the teen years. These Fibroadenomas are basically benign breast tumors that can often grow rapidly and can cause considerable discomfort. Most times these tumors are just left alone unless they become very large and/or cause a lot of pain. There is some thought that these tumors could be related to the hormone levels in the body but this has not been proven as fact. Simple cysts are hormone related but they differ from Fibroadenomas. There is an Expert Forum on Gynocology and you might post there regarding the fact that your Daughter has not yet begun her menstrual periods. The age for onset of Menses does vary so I'm not sure that this is something to be overly concerned about. This and the breast issue may not necessarily be related. If you could find a Physician who deals with Pediatric Gynocological issues you might see him/her but stay with the Breast Specialist for the breast issues. Kindest regards ....
p.s. One additioinal point: Questions in this forum are answered by survivors and other volunteers generally not identified as medical professionals.
If you still believe an Internet medical opinion would be helpful, you might post in the BC Expert Forum.
However, if you are not satisfied with the recommendations that have been made by the specialists who are treating your daughter, I believe your best bet would be to seek a 2nd (or 3rd, or 4th) opinion through in-person consultation for her with another, or other, top experts.
Once again, best wishes.
You consulted with someone in London, the "best biopsy specialists in Israel" performed your daughter's biopsy, and you have had your daughter examined at "the best breast clinic in Israel." The doctor and "professor of the department" have made recommendations to you. Presumably most of these experts have actually examined her, and have access to all of her medical and tests results.
Surely, anyone over the Internet, who has not even examined her or studied her full medical history, could not provide better information or advice than that which you already have available from all of those experts.
Best wishes to both you and your daughter.