I guess the flimsy justification here is that Quiet's ability seems to be not suit-based like Laughing Octopus or Snake's various suits, and more an Invisible Woman kinda power that comes from her and also affects her suit. More clothing requires more focus, maybe?

Kinda a convoluted way to get around a character dressing like Yoko, but I guess that's better than no explanation at all.

Well it's probably harder to make more clothing dematerialize/ turn it invisible.