It depends on her particular case, as with most things. However, if she had lymph nodes removed, she may have lymphedema. This is because when they remove lymph nodes, the body has no way of removing fluid build up. There are different things you can do for it. periodically raising your arm to allow fluid to drain. there are compression sleeves that would essentially pump from the bottom up.
I'm a breast cancer survivor and have been fortunate enough not to suffer from this. But i have been warned about it. she should not get needles or have blood pressure taken from the affected arm.
If she is wary about talking to her doctors, perhaps you can help by getting her permission to call the doctor yourself so you can ask questions on her behalf. My mother did this for me when i was sick because sometimes you get bombarded with information and need someone else to hear the information as well...
breastcancer.org IS a very good site also. explains things on a real level.
Try joining the discussion board at breastcancer.org and ask your question there. Sorry I can't help. Maybe someone here can offer info soon.