Q: We just started following the GAPS diet for weight gain in my daughter as she is just bones and is at the very low end of the weight charts for her age. She is 3 and still wears 18 mo clothing. Since going on the GAPS diet she has gained 1.5 lbs.
A: Have you ever tried "pediatric massage"? It's from the chinese/acupuncture school of thought, but it's for kids with appetite/digestive/growth issues.
Chinese medical docs do this on kids. It basically revvs up their immune system and gets everything working properly, including an increase in appetite, better sleep, and gaining weight if they need it. (An example is with a preemie born at 25 weeks, and by the time he was 3 he was caught up to his peers on the growth charts).
Let her lie on her stomach and at the very small of her back (just above butt crack) pinch the skin with your thumbs and pointer fingers. push your thumbs in and pull your fingers out, rolling/pulling the top of the pinch toward you. "walk" up her spine, pulling a pinch of skin at a time.
She probably won't like it at first; I've had it done to me and it doesn't hurt, it's just really uncomfy feeling. You should do it 10 times in a row before she goes to bed. After about a week she should get to where she loves it: even asks for it. It should help a lot with the issues you describe.