Hard to determine from the context given here, but the classic ruling for the Kuudere was that it's allowed for them to smile more if, and only if, they had spent a significant time prior to that in cool mode (and equivalent for the Tsundere class). Later editions brought up that you had to constantly balance the two aspects, which made it more precarious and much more likely to cause breakups like what happened to your group. Honestly a bit similar to DMs who liked to force Paladins to choose between a Lawful and Good option, without allowing for a third option, and then punish them either way because they "broke their code."
TBH the DM had a pretty solid case on strict RAW basis; with the benefit of hindsight it was a bad move to allow the group to make their only face character a Kuudere before the 3.5 guidelines that made it explicit that the class only got its full Deception bonus in circumstances where stone-faced silence was advantageous, but even without that it was pretty obvious to everybody involved that that player had been playing fast and loose with the archetype to the point where as soon as she was rolling any Charisma check other than Intimidation it was like she was role-playing a Genki Girl (a class which, I add, the character had zero levels in). So from a strictly logical position it wasn't hard to justify the ruling, but the timing of it all during a climactic encounter in what was probably going to be one of the campaign's final sessions killed a lot of sympathy the DM might have had.
Funniest part of the whole affair was that I was the player who was the most sympathetic to the DM's ruling, but I was only really there because I was sort of a friend of a friend of a few of the regulars that I lived near and I had a car so I could give them a ride. And the Kuudere's player was not only one of the people I was driving to the sessions but was also the sister of one of my best friends at the time, so there was literally zero chance that I was ever going to stick my neck out for the DM to mount a "Well, technically..." defense of the ruling, especially when I was pretty pissed that he picked basically the worst possible moment to put his foot down.
My most vivid memory of the whole thing was watching this group of people I only kinda-sorta knew basically rage out at their soon-to-be-ex-friend, looking at my character sheet for Green Sonja the Half-Orc Barbarian with her -2 Charisma modifier and thinking to myself "Yeah, all of this shit coulda been avoided if I'd just rolled up a fuckin' bard."