My W is the same way, RL. She's always been very judgmental and critical of cheating. She's got a very black and white view of most things legal and moral. Except for when it affects her, it seems.
W hates driving after dark, or in rain, or especially snow. So, pretty much at all.... So she comes over, then doesn't want to drive home late. This is the second sleepover.
I so far have failed in that approach, but I'm keeping it in mind. I haven't been shot down, just haven't managed to give it a try yet.