Ooo, I certainly know how she feels. I've been there.
The best thing you can do if she doesn't want you to touch her is keep her mind off of it any way you can. Whatever she loves to do, do lots of it! Movies, television, video games, cards... and remember, even if her favorite thing is shopping (and shopping can really be painful when pregnant!) you can let her do some catalog and online shopping. Buy her some books or magazines if she likes those. Get her some crafts if she's into being "crafty".
Don't make her get up any more than she has to. BUT, don't let her stay on the couch constantly, either. I don't know how far along she is, but if she's getting close to her due date, as painful as it is she HAS to walk some, because that helps settle the baby's head and get her body ready for the birth.
Kudos to being a caring partner!
(edit) Oops, I just saw the post about 21 weeks. So yeah, she can be a little lazy now. Hehe. She needs all the rest she can get now while she's still relatively comfortable enough to do it, because once she hits about 6 or 7 months, sleep is going to be difficult to near impossible for the next 3 or 4 years. ;)