I have a friend who is always complaining about her husband! How can I tell her to cool it?

I have a friend that I met three years ago. I only knew her for a short time and I moved away. Well, we have kept in touch by phone and she is smart and I can depend on her when I need to talk to someone I trust. The problem is, she got married a year and a half ago and had a baby! She calls me nightly complaining and venting about her husband! I dont want to be rude, but I just cant take it anymore! I want to say "If you hate him so much, leave". I was wondering what some others may do in this sensitive issue!