Karolina is quite common, but Karola is pretty unheard of in Poland, although technically it exists as a name. The problem is probably it's too similar to "Karol" which is a male name.
Princess Margarete Karola of Saxony, later Princess of Hohenzollern was the third child of Frederick Augustus III of Saxony and Maria Anna of Saxony. Prior to her birth, her parents had a stillborn daughter named Maria Alix Karola. In both cases, they were likely named after their grandaunt Carola of Vasa, Queen of Saxony.