If her music is gone, all of that goes away and they could sue her like they should be doing.
My understanding of the DMCA safe harbor regulations is that they basically work just like SOPA was supposed to work, except on service scale instead of DNS scale, in that the service is supposed to take down content on accusation and not proof of any illicit content within. Furthermore, I also understand that you and the service in question (Steam/YouTube) don't have personal data of accuser necessary to sue for DMCA strike interfering with your activities on the notice, as it is actually not required to contain such at first - apparently some sort of contact data in case of service deciding to act on not guilty plea by the content uploader is required, but that's not sufficient to sue. If you have data claiming otherwise, please share.
Under assumptions above, there isn't really that much of a difference between getting taken down due to content that is claimed to be someone else's but was actually made for you, and getting taken down due to the very same content that actually isn't in your game anymore, or heck, any content that wasn't in your game ever. All are wrong, and with all you can't do anything about it at first if you're using safe harbors. Situation is somewhat different if your content redistributor is not using safe harbor provisions, but that appears to imply at the very least manual screening for the most blatant offenses, something that is not an option for YouTube, for instance.
Taking the music down can also be taken publicly as an admission of guilt, which is not really something you want to do, I think.
tl;dr: I think you're wrong and it's a bad idea though I wouldn't bet my body parts on it as I'm not a lawyer.