White is so old she deals with a hundreds year war and the long lasting repercussions like her toddlers were throwing a little temper tantrum.
I bet she saw right through Rose/Pink all along she didn’t question Steven’s appearence, she must have recognized the gem no matter the position or projection around it. White was just humoring her, like a mother joining in with their toddler’s game of pretend. She would’ve joined the corruption attack with an amused smile on her face. ‘Oh are we the bad guy in your little game? What fun.’ and then BAM! Hideously corrupted an entire race just for laughs.