Sela and
Selah are the same name if they sound the same.
Selah is probably sel-akh, and
Sela sel-ah.
Selah:
http://www.hebrewletters.com/item.cfm?itemid=1376 (boy ONLY)
I have to mention that I've never seen any of these names used.
Sela is a term often found in prayers, it indicated a pause.
The feminine forms of
Selah are Silit (
http://www.hebrewletters.com/item.cfm?itemid=3631) and Salit (
http://www.hebrewletters.com/item.cfm?itemid=5860).