Her title and name are given as 片腕有角の仙人 茨華仙（茨木華扇） in the comic, and she introduces herself as 茨華仙, so I think the best tag based on what's out now is probably ibara_kasen, and not ibaraki_kasen. (Touhou Wiki is not a useful reference in this case - I wrote that article, so you could say it's biased.)
However, all of the existing posts have been changed to ibaraki_kasen, and there are a couple of new posts using that tag, as well. I was going to change it back later tonight, but I wanted to document why somewhere and give people a chance to object first ... I'd say we want to alias one to the other (I'd vote for ibaraki_kasen → ibara_kasen for now). The alias direction may change later based on events in the comic.
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