A woman should be called a Tsaritsa (Царица). A Czar/Tsar is a man.
For that matter, why does the gender need to be baked into a title unrelated to gender? We don't have separate occupational titles for female engineers, taxi drivers, or astronauts, so why for tsars? Not trying to push any agendas here, just posing a question.
English also has "Empress" ("императрица" is what they were called formally) and it would be derogatory to call her King Elizabeth.