Just to be fair to Michelle but she did mediate in the Jeremy situation. She didn't go all out yelling and screeching, she told Jeremy he should not have touched Chloe's robe and he listened. With Perez I think she has given up pretty much, she has her tolerance levels and he's crossed them.
With regards to KH she does seem to have turned a blind eye on her but I think she genuinely likes her so I guess you forgive your friends and overlook their misdeeds a bit easier.
Just being devils advocate here
