Thanks everyone, my SIL really is a gem. I really love her, but oh goodness can she be stubborn. We tried to pick up the tab for her while she was down visiting aka babysitting me, and she only grudgingly let us treat her to dinner.
I get what people are saying about really not wanting stuff....and it's not so much that I want to get her stuff, as she doesn't need it. But I am thinking of having my son "make" her a little something, a drawing or two.....He's 21 months, so his drawing is more scribbles, but she will still like it. I also had a thought about printing her up a little albulm of pictures of the two of them together.
I think the crux of it for me, is that she is so bent on helping all of the other people in her life that she doesn't and won't take time for herself and won't accept help or thanks from the rest of us either (and in fact, has been taken advantage of somewhat by other family members).