Why did you let her in? When people arrive unannounced at my house, I tell them hi and bye.

You're allowed to turn people away. It's your house. Your privacy.

So you reminded her of your plans and shut the door in her entitled face, right?

Lock the damn door and don't let anyone in. it's your house. You're allowed to do that.

I take it you got the pretty sister and weren't into a pity threesome? Could have been a lot of "fucking moments" as you put it.

She needed company.

Here's what I'm more likely to believe. Your wife's sister pounced on an opportunity to hang out with her sister without the interruption of child obligations, and she may even suggest an impromptu girls night out. Yes, I'm implying you're officially a third wheel. This is why I support what everyone else is saying and SHUT. THAT. SHIT. DOWN!

That's when you say, "We're child free because it's date night. Goodbye, have a nice evening." It's not that hard

Bounce the bitch on out the door.

Just start doing it and she'll probably leave