She seems to be quite the master manipulator and great con artist. Based on what little we know of her story it seems like she has been doing this kind of thing for a long time. Though it was probably much easier for her to take on the Dr. Smith persona than anything else she's done. No one who she ran into seemed to know the real Dr. Smith and since she was let into the program (or since for them it seemed she was let into the program) I guess that probably made it easier for the others to accept she was who she said she was.