A dynamic character is defined as one who changes or evolves throughout the story. A static character is one who remains the same no matter what happens during the story. As far as Tally is concerned, she is a dynamic character because she starts out believing one ideology, but then toggles back and forth when she is presented with new information about what she believes. For Tally, it starts in the first book, Uglies, when she wants to conform and become pretty like all of the other kids she grew up with. In the first book, she learns that there are two sides to the Ugly ideology and the Pretty ideology. She has to decide which one she really wants to commit to, but she is captured at the end of the first book and forced to have the cosmetic surgery whether she wanted it or not. At the end of Uglies, it seemed as if she were comfortable with living outside of the "pretty" society and wanted to stay there. But by the time Pretties starts, she has forgotten what she had learned previously and changes her mind. In the second book, she likes her life in the city even though she was forced to live there and make changes.
The journey that Tally travels in Pretties pits her against both perspectives of living Ugly or living Pretty; and by the end of it, she seems to want the best of both worlds. Just like every teenager who is confused as to which direction to go in life, Tally tosses and turns between making a final decision until someone comes along and makes up her mind for her! Tally tends to change as she is forced to change. She can't be held accountable, really, though because each time she changes it is because some doctor goes in and changes her brain and body physically, which can be traumatizing and confusing for sure.