I personally think they have to get engaged at the end, orders by the producers. That's probably a well known secret. As for your point about how she doesn't know him, no she does not. But she obviously wants this to work. Why? I can only guess. There's something telling her that this will work, and I think that something is Chris himself. If he just told her things aren't going to change and she needs to accept that's who he is or leave, then I would agree with everyone. But she talked about her seeing those glimmers of hope, and he obviously tries to say the right things to her. It's clear he doesn't mean it and for some reason won't end it himself. Remember him saying that thing about "when do you except things will change" or whatever he said.
I'm not gonna lie, she is desperate. But I have sympathy. This whole "process" is humiliating for someone in her position. She put herself there, yes. I know, I know. But I still feel sorry for her. The whole point of the show is to find love, and I think she was sincere, albeit naive, about it.