Ζωναρού would be the feminine of ζωναράς; that is the word for “belt-maker”, but it is far more common as a surname than as a profession. The feminine is grammatically correct, but you’re right, -ού feminines are now regarded as pejorative, because they are old-fashioned, and in olden times women either didn’t exercise professions, or exercised looked-down on professions—or else the suffix denoted a professional’s wife.
- μυλωνάς > μυλωνού “miller’s wife” (known from the proverb “from the miller’s wife’s arse, one expects no orthography”)
- καφετζής > καφετζού “café owner’s wife; fortune teller reading coffee cups”
- (modern, but unfortunately also pejorative) στριπτιζτζού “stripper” (as a peculiar mélange of English, Turkish, and Greek: striptease + Turkish –cı > Greek –dzis + Feminine Suffix –u).
All of them with negative connotations.
What’s a less stigmatised feminine? All of them would be awkward, but ζωνάρισσα is the least awkward to my ears.