[name_f]Cecilia[/name_f] is magical and perfect sounding I think. It stands up the best to [name_f]Arabella[/name_f] and [name_f]Genevieve[/name_f], which have a rather stately sound.
[name_f]Cecily[/name_f] cuts some of its regalness and sounds more cute and bouncy, without being made-up. [name_f]Cicely[/name_f] would be a bit more flower-fairy. Either [name_f]Cecily[/name_f] or [name_f]Cicely[/name_f] fit in well with [name_f]Violet[/name_f].
[name_f]Celia[/name_f] doesn’t work as well for me as either of the other two.