The English translation sounds grammatically incorrect. Perhaps a better translation would be ‘you have not married yet’. Thinking about this makes me question if the Czech sentence is discussing a marriage or a wedding day. Could someone clarify?
It's discussing a marriage. Vdaná is an adjective and means "married". (The male version is zenatý.) I think, the English translation is correct - It means that the woman, at an earlier point, was not yet in a marriage, so not married yet. "You have not married yet." or "You didn't get married yet." is in Czech "Jeste ses nevdala." Is it clearer? (Sorry, I have no Czech letters on my keyboard.)
The English translation "You were not married yet" is fine, as is the alternative (which was accepted) "You were not yet married." The latter also appears to be the literal translation of the Czech sentence.
Does a language as old as Czech have grammatical rules established to deal with such a modern scenario?