Now that I googled a bit, it seems so. The only uses mentioned are medicinal, which seems to be why it was purposefully cultivated in Finland centuries ago. The Japanese variety might have been brought just for ornamental purposes here. Funnily enough I do know this plant well enough, I just didn't know its English name. I certainly didn't know people would eat it.
She's does know something as made evident by the mandrake. It's a good question why she didn't know this butterbur flower considering it's an ancient medicinal plant (maybe it wasn't in Japan?). But then again, she's still quite young and quite absent-minded, so who knows. I guess she knows some things well and others not at all. Apparently she didn't need to cook her own meals back home, she only made sweet snacks, so she wouldn't have known pure food related things so well.