Alexandra Feodorovna may have been born a Hessian (modern-day German) princess, but she is remembered as a Russian empress. The Russian word for empress (there were no queens in Russia) is царица, translated as tsaritsa. It is also written as tsarina, czarina, or czaritsa. Russian is a very complicated language, one that I speak in a very limited way, but the most accurate way to spell and say Alexandra's title is tsaritsa. That is because the letter "ц" is phoenitcally equivolent to the sound "ts". Nicholas was the tsar (цар), and their son Alexei was the tsarevich (царевич). The "cz" spelling still occurs in some sources, but I've noticed a movement toward the "ts" spelling is more accepted as accurate.
The word "tsar" is close to the German equivolent "k" - both taking their names from the Roman "Caesar."
Incidentally, the last German kaiser, Wilhelm II, was Alexandra's cousin - though they would later become enemies with the dawn of World War One.