I'd have to say shawl too.
But another thing that would be great is to buy her a tea pot and knit or crochet a cozy for it. Get her a nice tea mug with a matching cozy as well. Fill a basket with these items and give it to her as a relaxation gift. As a new mom, God knows your tea will cool before you can drink it all. Maybe a tea cozy would be nice.
Also, I've given bath mitts and scrubs. I actually made a bath scrub the apricot scrub to use with it. I found it all on DIY. Also, All Free Crafts has some good suggestions.
Check here as well for bath gift recipes.