The bane doesn't need to be scheme itself. Schemes can keep your bane card in your next draw often enough to deter or defeat the young witch. You would however needs to play the bane card, so you'd better hope that it is not embargo.
Good point. I am not sure how viable it is as a hard counter. It looks like a pretty good soft deterrent.
Buying enough schemes to keep the bane card in hand seems somewhat of a waste of time (unless ironworks, conspirator or peddler is around?). If a single witch buy makes you waste 4-5 scheme buys (and forces you to reserve one card and action slot each turn for the bane), then she probably did her job.
I mean, if the bane card is a terminal, you are not going to be happy anyway (because you prefer playing a powerful terminal each turn) and if it's a cantrip, just hoard those instead of hoarding schemes?