I guess it's subjective for the reader, I just didn't see it that way at all. Your playful flirty girlfriend is teasing you that you wanted to bang Katie, (an outcome she didn't mind in the slightest) - and she knew bringing it up would advance that plan with Katie. If anything I'd call her a great wingman, which is super cool because she's your girlfriend too.
If this comment isn't taken in a light-hearted flirty context, then why the hell would the player as mc be comfortable telling his gf he wanted to fuck another girl? I get that you're merely relaying the message and don't speak for yourself, this position is just bizarre to me.....like those players are okay telling their gf they want to fuck around, but get all butthurt when that gf teases them back?
Anyone, I love her character now, she seems like the ideal partner-in-crime for a porn game; fun, high-energy, high sex drive, outgoing, adventurous, open minded, mischevious.