Try not to do her reasoning for her.
Ask a question then shut up and make her do all the talking. Keep asking yourself if she is really answering the question you asked, or is she tricking you into a change of subject?
Give her a guilt trip for any tricks she tries. Feign being offended.
Remember that you don't need to justify leaving as you haven't actually left. You want her to justify remaining with a church with this infanticidal god.
Show her pictures of kids getting killed in wt pubs, especially pubs she raised you with and that she would have studied.
You need her to tell you she has problems with her beliefs and she won't do that if you are doing all the talking, so practice a bit of shut up.