This is a name invented in the recent decade(s).
The name Сияна (Sijana, Siyana) reminds me of another word, the adjective сияйна (sijajna, siyayna), and obviously this was the indended effect.
The adjective сияйна means radiant, shining:
http://eurodict.com/СИЯЕН+searchid-44213-ed_bg_en.html
The word is a cognate of the verb сияя and the noun сияние which exists in Russian with the same meaning.