Broken Home Kid!
A friend's parents are getting a divorce.
-Broken Home Kid
I wouldn't say, "I know how you feel," because how can any of us really know how someone else feels? But in a private moment, you can say, "I'm sorry about your parents. It must be hard for you."
You might add something like, "When my parents split up, it was awful at first, but then..." and share any advice about how you got through it. Just listening to your friend and letting her talk will help her.