Personally I have yet to coach girls that young, but 18s? Crack the whip! Hold them accountable.......Any player that does not take contructive criticism, or thinks they are really that good, isnt coachable .College coaches are not going to baby them at all! So, as they get older, you gotta get tougher as they progress. This isn't the only way, but it works for me. Coach during the week, manage on the weekend.