Why the ominous latin, ma’am?
Also, I was gonna bet the “Vampire who can’t die” has been with Ema’s family for longer, grandparents time maybe. To find out it’s the mom who fumbled the kill and Ema is probably attached to her like a family member (because the vampire saw her grow up) but still has this whole exorcist family honor thing going on… I’d bet the “split personality” is more of an internal battle of wants other than two completely different people inside of her fighting to take over. That would be a pretty normal response if you had a suicidal immortal auntie/older sister/whatever she sees her as who probably helped raise you.
The piercings themselves could be a form of self-flagellation and that’s why the mom was pissed at this.