What does the Bible say about people who see dead people?

I have a friend who sees people who have passed away. She can see, hear, and talk to them. This isn't fake, she really can. She recently told me that she sees my deceased grandfather at our ball games. She cannot see her mother who died a few years ago, which frustrates her. She isn't religious. Does the Bible say anything about this? Is this absolutely impossible? What does this mean about the people she sees, like my grandfather? Some would say that he hasn't crossed over into the after world. I'm almost positive he was saved though. Thanks.