Sayaka was a fascinating girl - they'd even hung out a bit, before, back then, when everything was so impossibly, disgustingly good. Junko had seen despair in her. Sayaka was despairing at her life, how hard and cruel and confining it was, and yet also despairing at how little time she'd have to enjoy it before being shunted aside.
Which would have been all well and good, and maybe even bought her a ticket out of hell, if Sayaka hadn't been so unbearably sweet and hopeful in the face of all odds. All her chirping about how happy she was, how much she loved her group and her friends, how glad she was to be where she was. It was all a mask, it had to be, but it was a good mask.
Junko didn't intend to let that beautifully repressed despair go to waste, even if she had to kill the bitch to let it out.
She builds a stage. Sayaka is most at home on a stage, right? She builds a judge's podium - oh, the judges love sweet, smiling Maizono-san. She builds a scoreboard - perfect student, perfect performer, she never worries about her grades.
Then she adds the blades and the knives and the springs that will end it all. And she hopes with all her heart that Monobear's camera will be able to capture that last look of despair in Sayaka's eyes as the trap closes shut.
It will be an absolutely magnificent performance.