Funky Grammatical Issues

For those who haven't figured this out yet, apikursus is an Aramaicized Greek word in its Ashkenazic (Eastern/ Central European Jewish) form. In Jewspeak, it means "heresy." An apikoris is a heretic, which, I suppose, is what I am, but I haven't been able to figure out what the correct feminine form of the noun would be. Imshin suggests epikorsit, which, as she concedes, is a (modern Israeli) Hebraicism. Opinions?