I for one don't think that Serini has been unduly insulting to the Order.
She was however needlessly insulting to the paladins, who I don't think had done anything to deserve it. I don't think it would stand out that so much if it were in combat, where insulting banter is expected. But it happened after they were her helpless prisoners. Taunting prisoners isn't really a big deal, but it just seems needlessly antagonistic, like taunting an animal.