She was a ghoul but the thing is that she did want out of it and at the time she was in Martinaise she was kind of having parallels with Harry in that she was trying to lose herself in drugs to forget her past. She was also on the run from the moralintern herself. AFAIK if you do arrest her she will be killed while in jail (you also have an option to give her to the sunday friend!!). Honestly I would say within the time of the story she's easily no worse than HDB. The only 'bad' thing she does is having sex with the mercenary and then lying to the cops about it. She does leave you a parting gift if you don't arrest her: a ballistics analysis showing the shot came from the island.