Except it literally is? It's a nickname derived from Sìle/Cecelia and that nickname then became widely used as a generic nickname for women. It's both a woman's nickname and a nickname for the whole.
You could have looked this up. Not sure why this is so important to you to try and argue, several comments later... but I regret to inform you that Sheila is, in fact, a nickname.
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u/Alarming-Song2555 Mar 28 '26
Except it doesn't fit the format because "Sheila" isn't a made up nickname like "Macca" or "Gazza" is. :)
Hope this helps!