Kristen claimed she was seeing a psychologist/therapist for years in Europe, and was helped greatly. In my opinion, her thought processes have not been normal since she returned. Her need for revenge has consumed her, and taken over her life upon her return. Her plans just keep getting worse. She already succeeded in her original mission, which was to drive John & Marlena apart, and she called Brady collateral damage, so he got pulled into it and got hurt, which hurt both John & marlena as well.
But Kristen decides she wants even more, so picks on a priest. Oh, she could have picked on Sami.......who also is Marlena's child. But no, she wanted the complete destruction of a priest, a man who never did her any harm. But then, neither did Brady. She doesn't care about that. She wants to hurt Marlena, that is all.
Eventually, she will be committed, is my guess.But before then, Kristen will get away with a lot, Because no one will believe Marlena, the pyschiatrist. It is too personal for Marlena.