I don't think it's the stock, and I also think it may be a non-issue all together.
Unless there is a true discomfort in the way the girls "hold" too see through the scope and fire, it may well be that's just how a gun fit's them. If a cheek is high on the stock, who's to say that hold is improper,?
I'd make a trip with the girls to a sporting goods store with a large selection of guns on the rack,,and have them hold several different gun's, granted you'll find many that are too long a pull and maybe a bit heavy, but just have them grip the stock and NOT the trigger and watch how they "cheek" the stock. Watch and look more than guide,,Do they have the shoulder an Butt in the right place? Bring a tape measure in case you find one they like and fit's good.
That 11 1/2" pull on the youth stock was too short for my boy even at 11, an girls can grow faster than boy's. If they have the hand in their face it may be too short,,,12 1/2 was better. An those adult stocks at 13 1/2 and 14 are too big for me!!