I'm pretty sure
Síle is the Irish version, but I could be wrong. My knowledge of Celtic names is rather new.
To be honest it looks like an "Irish influenced" spelling. Like someone wanted the name to look more Irish.
I think that is trendy over there. like
Éimhear vs
Emer. Both technically correct, but
Éimhear the more modern look-at-me-I'm-Irish version. Which I don't mean in an insulting way at all.
As for the name. I just don't like
Sheila. You'd think I would for the simple sound and vowel-heavy look, but I don't. I knew a poisonous
Sheila and my opinion is skewed.
Sheela and
Susheela I still love. The similar Hindu names.