Ciara pronounced "Sierra" or "See-ARE-uh" simply is NOT the same name by origin as the Irish Ciara pronounced "Keera" or "Kee-uh-ruh". It is a transfer from the trade name of a perfume made by Revlon that was popular in the USA, which was introduced in 1973. I haven't been able to find out how Revlon came up with the name of the perfume, but I think it's highly unlikely that they had the Irish name in mind, and that the relationship between the perfume and the Irish name is a pure orthographic accident. So there really should be separate listings on this site for the two different Ciaras, just as there are separate listings for names such as Colin, Bao, Aina, Aliyah, etc., that have more than one true linguistic origin. [noted -ed]
Revlon, by the way, wanted the name of the perfume to be pronounced "see-ARE-uh", but many customers said "Sierra", which is how that pronunciation became the common one in the African-American community. Other perfume or cosmetic names that have led to baby names include Chanel, Aviance, Toccara, and Coty.