It's up to you! But Millie is usually short for Millicent, Camille, or Mildred.
Millie Tirelli's birth name is Millie Vega.
The name Millie means highborn power :)
Millie does not have a clan name. During her warrior ceremony Firestar offered to give her a clan name, but she refused, saying that she had always been known as Millie and she didn't want her name to change.
Millie Stegmann's birth name is Milagros Stegmann.
Millie Jackson's birth name is Mildred Jackson.
Yes everyone knows a Millie
Millie Chapman's birth name is Gloria Mills Chapman.
Millie Zandi's birth name is Amelia Negeen Zandi.
Millie Baring's birth name is Miranda Louise Baring.
Millie Impolito's birth name is Carmella Maria Apicelli.
MEEL-lee is an Italian pronunciation of the name 'Millie'.
Millie Corretjer's birth name is Milagros Ninette Corretjer Maldonado.