Hi Drwho and welcome.
The thing is she is stuck in a harmful cult and has a cult persona and an authentic persona. Talking doctrine with her will bring out her cult persona and make her more resilient, doing fun things, hobbies and interests, and talking about no religious things will bring out her authentic persona.
The book Combating cult mind control by Steve Hassan, explains this further and helps people free their loved ones from cults.
Kate xx