Is that a question? There’s loads of things in tank that are capable of doing this kind of damage. But I don’t know if a Nem is one of them.
If so, this would tell me that the Nem stung her, and she swam so hard to rip her own flesh off. But frankly, I don’t think she would be capable of doing that if the Nem stung her that hard. I’ve seen wrasses and other fish that are much stronger swimmers fail to get away from Nem stings. Now if her flesh was weak due to an infection or something, that would maybe contribute to it.
While it’s possible, I’m more inclined to believe this is caused by something else. Example could be latent bacterial or fungus infections, similar infections that came in on recent rock/corals/fish acquisitions,getting too close to pumps, pests that came in on new or old live rock (I know of pests like a Eunice worm that went undetected for years), or even clean up crew members and other fish.