Hello and welcome to the forum. Thanks for the question. Sorry your friend is having this nerve wrecking situation. I understand. Please know that when a woman is called back, it doesn't indicate they've found something but rather they want to take a closer look. In fact, it is very common to get a call back to look and especially when a woman has dense breasts.
They make imaging a little trickier. Most often, the closer look results in being given the all clear. Even if something is uncovered in the second mammogram, it does not mean it is cancer. Macrocalcifications, benign cysts and masses can be present and not be cancer. So, they are taking the best care of the person they called back. Investigating things to make sure she catches any situation that needs medical attention. https://www.cancer.org/latest-news/if-youre-called-back-after-a-mammogram.html Do you happen to know her BiRad number which is what a radiologist assigns to her imaging. Try not to worry as again, things most often turn out to be a non cancerous situation. Let us know.