Everyone always says "call me if there is anything I can do". No one ever calls to say "come over so I can yell/cry/discuss the painful unfairness of it all to someone besides my closet wall". I think it is hard if you aren't close to her already, but I'd think of something to do with her - maybe walk around the lake, something like that? then suggest it to her with a specific day in mind. You could renegotiate day if it didn't work for her, but if you don't have a specific place/day, it is too easy to decline politely.
So many people avoid you in situations like this. I think just having someone to go get a coffee with might be a nice break for her. Just regular things that all of a sudden fall off your social calendar because people are afraid of making you cry.
If you knew her better, I'd suggest doing the chore that he did - pull the garbage cans to the curb on Thursday night, or whatever it may be. Because taking over those things that were "his" might be really hard emotionally.
It is nice of you to want to help her. I think a note with a personal memory of her dh (if you knew him/have one) is a really nice touch - instead of just signing your name to a sympathy card.