I think a gift certificate to acupuncture, or to a local mid-wife (you could call ahead to see if you think she'd like them and they could help her) would be nice.
Oatmeal was the only thing that worked for me for one pregnancy -- plain. Yuck! I am only starting to be able to cook it again for my kids 8 years later!
A good novel to keep her mind off it?
Natural, unscented bath and body products? I like www.passionatehomemaking.com for those kinds of things. We use lots of her recipes.
A quiet toy for the older child to play with when Mommy just needs to lay down.
A nice, dark towel that she can clean up with after she returns meals. Or a pretty hair tie that would keep her hair out of the mess. On the more humorous side -- a pretty padded toilet seat to lean her head on. :)
Just a little pretty she can look at and know you love her. I had a friend send me a little water globe. She didn't know what to do, but just wanted me to know she cared. I still have it on my bedside table, even though it's been broken through our many moves. To this day, it's one of my most treasured items.
I feel her pain! You're such a good friend! Sometimes there is just nothing at all that will help, but knowing someone cares and loves you is such an encouragement. Thanks for being such a good friend!