Well then I have to say, if she is dating her and doesn't want to marry her/bring her in to live with you full time, then the benefits you could think of, such as extra help with child care/housework, and 24-hour company probably just aren't enough of a selling point to give up the privacy and independence she can get by having some time to herself in your house.
I think that after dating somebody for 6 months I'd have a pretty good idea if I wanted to live with them or not. I'm not sure somebody could convince me I wanted it with a list of practical reasons, if I didn't already want it.