They obviously read her mind, or the Columbia's computer banks, regarding what a human being was supposed to look like, because they gave her the illusion of being a normal-looking human being. But what you're talking about is actually repairing the physical damage that had been done to her body, for real. That would require some rather specific medical and anatomical knowledge. Vina's mind may not have contained that knowledge. It's also possible that Columbia's computers did not contain that sort of information either or that, if they did, they were destroyed in the crash. So the Talosians did the best they could: they patched her back together as best they could figure how, and then used their power of illusion to let her see herself the way she originally was.