"you can pay the same that your paying now to your current roommate, I wouldn't ask you for anymore than that" So, since she already has a roommate that could be quite low.
The more I read, the whinier she gets.
Good catch. I just read it as he has paid off his mortgage but I think I was wrong to read it that way.
However, I don't think she should pay half his mortgage. First of all, what if his mortgage is rather high, and half is more than she'd be paying in rent at an apartment of her choosing? I think she should pay something, and not some piddly amount like $200/month. But I also think he should cut her a break for a couple of months while she looks for another job.
But I also think rent isn't the issue. She wants to move in with it leading to marriage and babies, and she doesn't know that that is his plan. They need to talk about the future.