How many girls do you have trying out? We can talk about methodology and weighting all you want but at the end of the day the discussion is still purely academic. Why not keep notes on each individual girl: what each does well, what they need to work on.
Also, you don't have to limit it to strokes. Don't forget about things like work ethic, attitude, competitiveness, etc. Working with teenage girls is tough because they have such different personalities. Teenage boys generally are good at taking orders and will run through a brick wall if you tell them to, but with girls you have to know what style of coaching each individual responds best to.