My answer from the Facts board
in reply to a message by Jen Demars
If you call her Cesca or whatever you want her to be called, people will call her that. As soon as she's at school, this might change though, but then she is old enough to decide what she wants to be called. My mother thought Cerridwen (see Ceridwen) would discourage nn's but I'm now mostly know as Cerri at school. :-)