My 26f sister 19f has been flirting and kissing a 35 year old man and keeps asking for my advice

My (26f) sister (19f) is trying to become a police officer. She is currently in a civilian role in the department but is actively working towards becoming an officer next year. She recently told me that she has been flirting with an officer (35m) who has been helping her in her training. She has said that they go on long walks together often, and talk about God and the Bible often (they're both very conservative Christians). She also says that he is married, but that he claims that his wife has cheated on him throughout their marriage (2ish years) and that his wife is abusive so they are getting divorced in August. She has asked for my opinion, and I have tried telling her that this is very dangerous for a number of reasons, but she keeps telling me that she's smart and knows what she's doing. Today, she told me that he kissed her and that they made out. I know she's an adult and can make her own decisions, but adultery is a huge no no according to her religion and she continues to ask me what I think but then push back anytime I tell her what's wrong with it. How do I respond to her when she asks for my opinion but then pushes back when I tell her how dangerous/inappropriate I feel the situation is?