As far as I know, its up to each school and coach how they award letters. When I was coaching high school, it was my philosophy that any girl who spent at least half of the season with the varsity deserved a letter. It is the coaches' decision whether the girls actually played or not in games ... but if we picked them for the team, and they were there for every practice and game and gave it their best, then they deserved a letter regardless of their talent and playing time.