Actually, I believe "Sile" is the most common Gaelic spelling of the name we in the US know most commonly as "Sheila". "Shelagh" is one of those versions of a Gaelic name that has anglicised the spelling, like Enya/Aine or Eavan/Aoibheann.

Connie is another name used in Ireland for males that is essentially a female name the other side of the pond.