When you don't use someone's preferred pronouns, you marginalise the whole trans community -- even if the person you don't want to respect is indeed a monster.

People have certain characteristics about them that are immutable. That Challenor is a pedophile does not change the fact that they are trans and uses she/her pronouns. We can attack her on her actual crimes, and not on perceived crimes (of not being trans enough or, as it seems in this case, that being a pedophile forfeits any validation towards gender identity).