I looked it up...it is German. My little sister is named Katrina and she was born in Germany when our father was in the military.
I say it has Slavic origin. I just googled Katrina Müller (the most common German family name is Müller) for sites from Germany and got three results. I then googled Katrina Schmitz (also a very common name) and got two results. With Katharina Müller I got ca. 9.000 sites (without the doubled links, say 5-6.000).