Due to Alice's enormous size, she's treated as a monster by everybody, despite being just a very big girl. The goverment wants to kill her even if she hasn't harmed anybody. This prompts Alice to become resentful and hate the human race, going in a rampage, ravaging several cities in the process, until she's taken down by military forces.
Due to the Square/Cube Law, Alice's massive size causes her serious health problems and even a small fall for her causes massive injuries; Scientists realise that unless this is reversed soon, she will most likely die from her condition.
Alice uses her size to help people, such as rescuing people from burning buildings, capturing criminals effortlessly and making her town a better place, earning everybody's gratitude and respect.
Or, to compensate for the Square/Cube Law, Alice becomes exponentially stronger, meaning that she can support her own weight.