At a guess, that's her real name, while the Units list shows a cover identity (or possibly vice versa). At a further guess, she's a migrant who was out spying for your civ when she got "drafted" into joining your fortress (It's a known bug that migrants can come with fake identities and jobs, and at least at some time DT showed real identities for some units that "should" be under cover [I believe vampires were fixed a long time ago, but buggy migrants are new]).
Yet another guess is that she is innocent, as it's usually the "witness" who's the real vampire (and quite frequently the mayor). It's not that uncommon for vampires to "witness" A committing the crime of draining B, only for A to be the next one to be drained (Help! a vampire group attack!!!)...
It should be noted that visitors can be vampires as well. Currently they're announced as such in the announcement, but nowhere else, and it's easy to miss them. If you do, it's almost impossible to find out who the visitor vampire is without witch testing (various tests resulting in innocents getting killed by the tests, while those who are not killed are vampires).
Check the wiki for finding out how to identify vampire citizens.
As indicated, vampires always operate under a fake id, but both DF and DT should roll with that (there was a bug with petitioners, where petitioning vampires were petitioning under their real names, but that's been fixed).
Avuz was the cover-identity--Ino Nodoti was her real name. Fortunately, there were multiple witnesses in each case, and like I said, Dwarf Therapist confirmed this. The thing is, I could place labor assignments, but could not draft the character into the military or other role (including Tavern Keeper), nor could I add her to a burrow because I couldn't find either her fake ID or her real one in any of the searchable lists.
UPDATE: It turns out that, while I couldn't search for her by name, I was able to search for her by
profession. Typing that into the search brought up all my gelders, and there she was! Now I just need to figure out how to get her out of the way...