I'm sorry to hear Herbert isn't doing well.

This site is very good, here's a page on health:
http://www.aracnet.com/~seagull/Guineas/ailments.html

It says to keep a sick piggie warm, with extra hay to insulate him.

Maybe if your daughter pet him he would be happy. Or if he doesn't like being pet, then maybe just talking to him for a while. I hope he does okay.