copyright claim? What kind of stupid shit- song covers are absolutely allowed and considered transformative content.
That said, I know exactly what this is...
Youtube does not care for its creators, and if anyone files a claim they give them your money first (or delete your video first), and only investigates the claim later if anyone appeals.
But to appeal you apparently (from what I heard) need to go through a legal process where you have to prove your identity, and apparently this is forwarded to the claimant. So people use frivolous copyright and dmca claims to get the identity of (and often dox) various anonymous creators on youtube, such as vtubers or the like. Or so I have seen ppl say (who went on to say that the vtuber in their example were lucky because they had an agency that shielded their identity, as it allowed the corporation's legal identity to be used, rather than the individuals).
So whoever did this is clearly just trying to force her to out herself?
edit: found the source! Or maybe not? this one says it was twitter outrage that solved it, not agencies. But I suppose it is just rampant enough there are more than one~
youtube