This comment just made me wonder if Shirley is a female bastardization of Charles through Charlie…

I gave it a check (Wiktionary is surprisingly good for this sort of stuff), and reality is even weirder:

“Shirley” is etymologically equivalent to shire + ley. It was initially a habitational surname. Then based on the 1849 quote it was used for some time as a masculine first name. Then as a feminine one.