Remember that your goal is to be helpful, because you are an awesome and caring partner. When you remember what your goal is, and you already know that simply listening/allowing a safe space to vent is more helpful than offering solutions, then hopefully it becomes easier. Also remember to give your partner some credit-- there's a great chance she's already thought of some solutions. That's not the point. She needs to get some stuff off her chest.
If you're ever unsure-- here's a tip I've heard before that has worked wonders. At the beginning, just Ask her if she would like you to listen, or offer advice. :) Then you know from the get go what's needed. I've heard employing this simple technique has eliminated many a would-be-arguments, and makes everyone feel more comfortable with expectations clear.
Good luck to all of you out there. <3