Ariana's Empath powers, if one thinks about them. She cannot turn them off, leaving her to feel strong emotions from anyone. And depending on their strength, they can override her emotions and lead to outrageous behavior. She also suffers what can be mistaken as an allergic reaction, when someone nearby takes a mood-altering potion or uses such a spell, like the Cheering Charm.
In this universe, Snape's loving parents were killed by werewolves. Sirius knows this; he was, in fact, right there when Snape found out. Remember that whole "try to get Remus to kill Snape" prank? This fic somehow made Sirius look even worse for doing that, though the writer doesn't seem to have realized it.
Ariana plans to work at St. Mungo's upon leaving Hogwarts, wanting to become a healer and help people, with her Empath powers. Given how she tends to faint or have something akin to seizures if someone nearby has their mood and emotions altered, wouldn't that be a horrible disadvantage for that job? And what about overly aggressive patients, which could override Ariana's emotions and cause her to become a menace to other patients and healers?
Yes, but Ariana fainting and having seizures is actually pretty common in the fanfics themselves, because they make everyone fret over her and draw attention to how "noble" and "selfless" she is, so it makes sense Ariana would continue to want to do that in her adult career.
