Her first reaction is shock. She didn't think Princess had it in her. Next, satisfaction. Here is proof that she never was any better. All that talk about what we can and can't do was just a lot of hot air BS in the end.
There's a sudden desire to apologize that's so unnerving in its sheer insanity that she almost laughs.
It's too late for that anyway. She's always ridden in the front car of the roller-coaster. There's time for one more plunge.
She gives B her best Fuck Me smile and sails over the edge to her death.