Not too many models change their performance much. We have had Gloria in 3 shoots over a year... she was amazing when she debuted. Her second visit, being petite as she already was, she was pushing to the gaunt side. Now her third visit, a year later, you can see she has matured some and looks fantastic.
I should probably answer your question, she does not seem to make any major changes :P If you are trying to save on credits, I usually try to figure out which outfits will be most appealing and go from there.