Just be there for her. Sometimes you don't even have to say anything - just a hand and a shoulder.
She will need some time alone, so you can offer to babysit. Or she may not want the little one out of her sight. But you could offer to watch the child while she takes a bubblebath or does something for herself.
After my husband's death, I did ALOT of my crying in the bathtub where the kids couldn't see me. I don't mean the occasional tear - the kids need to see that so that they know that it's ok to be sad, I mean the gut-wrenching tears that you have to cry in private and that you don't want the kids to see because it will scare them.
What I also found is that people are around after the funeral. That first week you are so busy that you don't have time to fall apart or feel lonely. But as time goes by, people return to their lives and she'll be left - alone - to pick up the pieces of hers. THAT'S when she will need you the most. Just drop by with a snack and share it with her. Call her and say let's go to the park. It doesn't matter what you do, just that 6 months, 12 months down the road, you still do it. Doesn't have to be everyday, but at least maybe 2-3 times a month. You'll see when she is getting stronger and ready to move on.
It's been 8 months since my husband died, and I don't think a day goes by without thinking of him. But not all memories are sad memories. We sat up til 1 am the night before his funeral, remembering and laughing. He left me a 6 yr old son that is a carbon copy - both endearing and frustrating at times. Most days are good days, but every once in awhile it still all catches up with me, and I just sit and cry all day. (I'm fortunate that we had started a home business together and I have the luxury of being home all day without the kids.) I do find that my heart is much more tender. I don't think I've managed to watch a single Christmas special this season without crying.
It doesn't state where you are from. I'm near Peoria, IL. Methodist Hospital's Hospice Dept here has a good grief program - although some of it's designed more for the children. But they've got a list of resources/contacts. Many churches have grief ministries/support groups.