This is a rare female form of Cassian (KASH-in, though KASS-ee-an is accepted), Cassius (KASH-us), and the Roman family name Cassianus. It is of Latin origin, meaning "hollow, empty." The girl's name Cassiana is pronounced KAH-shah-nah, KASS-ee-ah-nah, or KAH-see-ah-nah. Cassiane/Kassiane (KAH-see-ah-neh) and Cassia (KAH-shuh, KASS-ee-uh accepted) are other female forms.
Recorded in the years 1992, 2000, 2005, 2006, 2008, 2011, 2015, and 2016 (5 births) never more than seven times in a year, the baby name Cassiana is definitely rare. The spelling Casiana was only used in 1996 on 7 girls and 1998 on 5, and there is no recorded spelling of Cassiane. The spelling Kassiana was used in 2011 on 5 and 2014 on 6 girls. Cassia was used 61 times in 2015, making it the most popular option. Although these are rare feminine names, they do have a nice history of use and a broad range of countries it is used in. However, I do think people confuse Cassiana for a smoosh of Cassie/Cassandra and Ana/Anna, or think it might just be a form of Cassandra. Cassiana and Cassandra do share the Cass start, but one is of Latin origin, the other Greek. By the way, Cassandra means "shining upon man."
Cassiana is a genus of moth, and Cassia is used in the botanical name for Chinese cinnamon, cinnamomum cassia. Also, while there are several male saints named Cassius and Cassian, there is record of Saint Cassiana the Melodist, who was born in Constantinople around 800 A.D. and known as a great beauty and very intelligent. She was courageous, and she wrote poems and music under her own name - something only one other Byzantine woman did in this time period (she was Anna Comnena). The same saint is also referred to as Saint Cassia/Kassia, Cassiane/Kassiane, and Kassiani.