You have a few things in your favour. One, the series is cancelled. So there are a limited number of episodes, she will run out one day. Last winter when I was sick, I started recording reruns of Law and Order SVU. After quite a few months of them never running out, I looked up how long the show was on the air. Turns out 18 years. But even at that, I reached the end of of them.
Second, the series will run out. Oops already said that. But if she starts to watch them over, then you need an intervention.
Netflix gives people the opportunity to see all the episodes quickly, and without ads. I do remember the protaganists slept together, but they did get married. Definitely not Christian, but then, what TV show is? Even that show with the pastor, came up with a lot of humanist garbage, which is why I stopped watching it.