If the buffet pricing doesn't fit your budget I'd avoid them. It seems cruel to have a child watch everyone around her eat as much as they want and not be able to have any. She's on vacation too and that would simply seem like a punishment to me. I just couldn't put a child through that.
Actually, SHE is the one who wants to go to Biergarten again, but not eat there!

She just WANTS to sit through it, and "maybe" just have something to drink. We have gone to Biergarten every trip, but she was always a "child"; now that she's an "adult", $20 seems a little steep to just have her watch and eat mac n' cheese.
We'll probably just skip buffets this year until she gets a more adult appetite! Thanks for the replies!