What Causes Shoulder And Armpit Pain With Soreness And Swelling?

hi Doc, my mother is 67 yrs old and past two weeks she was complaining of pain near shoulder region and under the arm pit and now its like some swelling has developed and the area looks sore, more on the right and slightly on the left. on pressing the sore area, it pains, today we visited our orthopedic surgeon and he suggested we get a mammography done. Already her mammography was done 5 months back and it was normal. Doc also suggested we do a sonography of that area to find out. can you please suggest what could be the issue? thanks.