I would say do as Barny suggests and have her try on each piece. It will hang/measure differently based on her shape and the fabric content. And the hemmer she refers to is a godsend! If you don't have the hemmer, have her point to a spot on the front of the skirt then measure up from the floor to get it even all the way around.
If she's not willing to do that then do as Betty62 suggests. Good luck. Sounds like a nightmare - and I have to hem just about every article of clothing I buy!