Well, my cards are a sheet of 8 1/2 x 11 cut in half, so maybe some of that size cardstock for bases. Other than that the only "necessary" stuff would be stamps and ink. And maybe some white cardstock for stamping images. She could add some ribbon, buttons, brads, etc. for embellishments as she moves forward.
She could also sign up for a class at an LSS, or go to
www.stampinup.com and find a demonstrator in her area and maybe have a workshop or sign up for a class through them.