Just listen.

Also, in a couple of weeks or a month, people will stop calling to check and see how she's doing. That's where you can do the best thing for her, call and ask how she's doing.
When you lose a loved one, you tend to get swarmed by people at first, then they sort of get back to their usual lives and forget that the person grieving is still in pain. It feels so good to know that your pain hasn't been forgotten; that someone remembers what happened to you, and that they're still willing to lend a shoulder to cry on.