I can't answer so much on generalities on this one, as it probably depends on the the person. I've personally had people say this in different circumstances (not always work), and sometimes it is believable and sometimes not. Thing is that I didn't necessarily think along those lines until they brought it up.

I'd say if she seems to be really uneasy (and you might not tell, most women will try to just be polite), you can try adding it in. Probably unnecessary if you've put the why's of it upfront, though. If she says no, you can always add a little more about what you wanted to talk about, and tell them the offer is open if she'd like. Well, in your own words, and using simlar language as you would with any other coworker and stuff.