Breast Cancer Treated, Developed Blood Blister Under Eye. Are They Sign Of Low Platelets?

My sister has just been treated for breast cancer ,& has finished her chemotherapy recently. She is now taking Tamoxifen ,but suddenly developed A large blood blister beneath her eye for no apparent reason. Her cancer doctor told her to contact her G.P whom she also told that she had been having stomach pain during her treatment,but thought that it was treatment induced. The GP is now giving her extra blood tests. A friend whose father died recently of cancer,said blood blisters are a sign of a problem with platelets(?) Should the cancer doctor see her immediately,rather than waiting 3 months& packing her off to her GP?