I think the Iceheart thing actuality makes sense, She is the leader of a group of sympathizers of enemies of the Holy See, so they have little reason to humanizing her. DEhumanizing Ysaile on the other hand offers many benefits. After all, whose side will people take, that of the religion they followed for a thousand years without knowing the real reason it came out, or a cold blooded heretic who openly aides the enemy?
Names and monikers can be an effective propaganda tool. Calling her a priestess in a theocracy would make look seem more sympathetic than effectively calling her a cold heartless bitch. The intentions of the people using the name (Thordian and his Knights) which are also clear, are also a factor.