The things Cat has to pretend to ignore keep getting more and more ridiculous.
Like, the first time she comes into Kara’s office unannounced, she spots a but of the cape sticking out of the file cabinet, and just ignores it.
The next time, the cape is tossed on the sofa, and Kara’s back is to the door as she buttons up her shirt.  So Cat makes a big deal of “I didn’t know anyone was making these?  I wonder if we can sue.  I should get legal to check into that.”
The third time Alex is feel stripping an alien rifle on Kara’s desk, while Kara is in Chicago getting them lunch, and Cat’s just like, “When your sister gets back, tell her I need a moment.”
The fourth time, J’onn J’onzz is standing there in full martian glory, and Cat is just like, “An interview with a Martian?  Impressive, Kara.  I’ll expect a draft on my desk first thing in the morning.”
The fifth time, Kara is hoping on one foot, in full Supergirl costume, because the zipper is stuck on her boot, and Cat just pauses for a moment, and once she’s sure Kara is in the process of taking the costume off, and not putting it on, she’s just like, “I really wish Supergirl would let us sue whoever is making these cheap knockoff suits.  The quality really is terrible.”  She helps a speachless Kara with the boot, and is then like, “Whenever you’re done with your cosplay… thing, I really do need the proofs for that article on the transcontinental bullet train proposal.”
The Sixth time, Kara’s trying to put the suit on, but the zipper is bent, and she doesn’t even notice Cat’s there until Cat bats her hand away, and pulls the zipper up.  “Really, Supergirl.  The quality on this isn’t much better than Kara’s cheap knock off.  If you like, I have Donatella Versace and Jimmy Choo on speed dial.  She could do the outfit, and he could do the boots.  By the way, do you know where Kara got off too?”
And it just turns into this weird sort of game of chicken, as two who will crack first.  And Kara keeps doing more and more outlandish things, just to see what Cat will pretend to ignore, and Cat loves it because she just keeps coming up with more and more ridiculous rationals for why Kara is doing something, or why Supergirl is doing something.  And of course, Kara breaks first, and Cat is totally, “Don’t be ridiculous.  I’ve seen you and Supergirl in the same room together,” with this huge smile on her face, and she teases Kara for another week before admitting she was fooled for like, five minutes by J’onn’s impersonation.