Hannah is Sid's younger sister. Despite her brother's antics, she appears to be normal. She loves her dolls, although Sid normally ends up mutilating them in one way or another.
Sid first takes Hannah's Janie Doll after he comes home from Pizza Planet, and swaps its head with Sid's pterodactyl, effectively scaring her. She then reports him to their mother while Sid tries to convince her that she is lying.
Later, she finds Buzz with his arm broken off. Thinking this to be just another toy abused by Sid, she borrows him for her tea party as "Mrs. Nesbit" by dressing him with a pink apron and hat (similar to Mrs. Potato Head's). The other dolls at the tea party are headless dolls that Sid has previously wrecked (Buzz calls them "Marie Antoinette and her little sister").
Much later, Hannah answers the door, not knowing that Ducky, one of the mutant toys, has rung it as part of Woody's strategical scheme to save Buzz from Sid. Soon, Sid's pet dog Scud, who is chasing another mutant toy, the speedy Frog, rams into her, knocking her down as he exits onto the porch. Annoyed at Scud for his stupidity, Hannah closes the door in Scud's face, locking him out.
When Sid becomes frightened of toys after his toys come alive in front of his face, Hannah takes revenge on her brother by shoving her new doll Sally (apparently a replacement doll for Janie) into his face and chasing him into his room, trying to scare him even more.