The question came up and while a lot of folks had answers, they actually sounded like opinions or guesses. So I thought I'd consult the resident experts here.
3rd Base Coach wrote:I am not saying that I am an expert but I do read the rule book.
page 194 in the CIF Southern Section Blue Book - #2514 Outside competition by an Individual :
During Individual's Season of Sport - A member of a high school softball team may not, during his or her season of sport, compete for an outside team in the sport of softball.
A 14u team may play during the high school season but a high school softball player playing for a high school in the CIF Southern Section can not play for ANY other team except her high school team.