Greta is a minor character who only appears in the 59th book-The Haunted School.
History[]
The Haunted School[]
The girl Greta first appears at the start of the book when the main protagonist Tommy goes to get two cans of red paint from the Third Floor as she's standing the middle of the hallway, outside the gym and he crashes into her while hoping to impress Thalia, sending them to the ground and angrily, she shoves his hand away when he offers to help her up and at first as she looms over him, he thinks she's going to try and hurt him for knocking her to the ground but she angrily states she was merely walking home and heads off without hearing his apology.
Later on, when Tommy heads back to the gym and tells Thalia about bumping into the strange girl, she informs him who she is and that she's a really weird person and Tommy should stay away from her.
Later on in the week, when the kids are in class and their teacher heads to the office to reply to a message, several of the kids start goofing around as Greta swipes Thalia's lipstick much to her annoyance and starts tossing it around the classroom, resulting in a fight between the two with Thalia almost having a nervous breakdown, nearly being reduced to tears trying to get it back as Tommy stands up to Greta and makes Greta give it back to her before the teacher returns to the classroom.
Later on, during the night of the local school dance, Greta arrives with the local band called Grunt and while joking around with the other band members, rips one of the posters Tommy, Thalia and Ben were working on, forcing the two boys to head to the Third Floor to get some tape as she merely laughs on the matter.
Finally, when Tommy and Ben are stuck in the strange colorless dimension Grayworld and one of the kids mentions that only one person, a girl managed to escape from the realm after 50 years, Tommy suspects it has to be Greta due to her bizarre physical appearance, wondering to how she escaped and why she didn't return for the others but his assumption proves to be wrong when the elevator door opens up as Tommy thinks at first, it's Greta but in reality, is equally shocked when Thalia herself appears and reveals herself to be the one who really escaped from Grayworld.
It's implied at the end of the book that Greta is also sent to Grayworld along with all the other kids from 1997's Bell Valley Middle School by the evil photographer Mr. Chameleon, the same one who imprisoned all the other students from 1947.
Physical Appearance[]
Greta is described as being really tall, with broad shoulders, tough-looking and resembling a woman wrestler as she constantly dresses in black, has solid gray eyes and white-blonde hair which may be why Tommy easily suspected her to be the one to escaped Grayworld.
Personality[]
Greta apparently is known to be sort of a bully to most kids as she both bullies Thalia and Tommy but otherwise, not much about her is really known.