What would you think about a secretive friend?

I am talking about a friend who isn't forthcoming about her life. For example, she said her brother is an architect. He must have gone back to school, because the last time she mentioned him he was a waiter. She also mentioned her nephew. I have never heard her speak of her nephew once.

Why would someone be so secretive about the basic facts of her life and the people around her? How can I get her to be more forthcoming?

We go a ways back. We talk on the phone regularly (we don't live in the same place) and send each other presents every Christmas but we aren't super close and she only ever contacts me at the same exact frequency that I contact her.