Complex sentence: She was overweight, with the nickname'Hefty Hanna', and after Alison Dilaurentis disappeared, Hanna lost her weight and changed her style, which seemed similar to Ali's, with the help of her new best friend Mona Vanderwaal.
Split into simpler sentences: She was overweight, with the nickname'Hefty Hanna'. After Alison Dilaurentis disappeared, Hanna lost weight and changed her style, which seemed similar to Ali's, with the help of her new best friend Mona Vanderwaal.