I've never got why people are so one or the other when it comes to Winslow's corruption. It's always either Blackwell didn't know or care what was going on, or that she was a hyper evil embezzler personally covering up Sophia's actions.
We know for a fact that the PRT pushed her to go soft on Sophia, but I've always assumed she was just generally apathetic. Given what happened to Taylor was based on real life bullying (that I assume wasn't enabled by government conspiracy), it's not as if Blackwell would need to be malicious to let Taylor get harassed.
Even if Blackwell was a sociopath, after the locker she would have reason to punish the trio and make sure something like that doesn't happen again. If only so the school doesn't actually get sued.
She was a generic shitty principal that didn't care what happened to her students so long as police or lawyers weren't involved, but was willing to ignore more than usual with Taylor because she had a reason not to punish Sophia.