I definitely prefer
Sheila, especially for a real kid. It would be unique for this generation, like you said, and
Sile would be mispronounced and misspelled all the time (people have a hard time with my name, and that's annoying - I bet
Sile is a lot worse!). The spelling also reminds me of bile, not a very pleasant association.
Sheila is nice, though, and refreshing on a kid.
Sheila RosalindSheila BryonySheila DamarisSheila Valerie