The woman Marcy was painting was herself. Though she was taller, thinner, better endowed... oh heck, she painted a portrait of herself that could easily grace the cover of any Playboy or Maxim magazine.
Ty could certainly appreciate good art, and Marcy was talented, but Ty realized that he wanted to see this dream girl come true. SOooo.
Still not letting Marcy become aware of his presence, Ty placed his hands on her shoulders. Concentrating on keeping his powers at a slow pace, he started transferring elements of Marcy with her two dimensional creation.