I am a fashion designer by trade, Poser would be good as a template to draw fashion illustration with, she could pose the model and then import the render into Illustrator or Photoshop (or whatever) to use it to draw her fashions over if you will. But as far as creating the actual clothes themselves, she will learn pattern making through specialized CAD software ( Gerber, Lectra come to mind). Learning to create 3d clothing would be of very little use to her in my opinion, it is relatively complicated and outside of the texturing bears no semblance to the craft of patternmaking.

Dominique Digital Cats Media