Sarah is Ed's younger sister who tends to be bossy, spoiled and short-tempered, only acting cute and charming when it serves her. Sarah has Ed's unending loyalty and obedience, mostly due to her constant threats of tattling on him to their mother.
She is a loud and controlling spoiled brat who despises her brother and his two friends.
She is very quick to anger.
She reacts to her anger through brute strength and extreme violence.
She lacks in empathy (Even towards Jimmy) and intelligence (Even to the point that Eddy, Jonny, and even Ed can outsmart her sometimes!)
She is so aggressive, manipulative and ferocious that her older brother fears her, and she refuses to accept the undeserving love and affection he gives her.
She mostly uses her strength to abuse the Eds and some other people.
She was even once mean to Jimmy, her best friend in the episode "One Size Fits Ed" for no good reason at all.
She never shows kind moments (Minus the boomerang effect in "Hand Me Down Ed".) to the Eds at all, even Kevin has his kind moments, but not Sarah!
She does not have a decent reason (minus the whole scamming thing) to hate the Eds, while Kevin and Jimmy had their good reasons to hate them.
Despite her negative qualities, she never gets punished or called out for her actions.
She also gets mad at Ed when it's not his fault. For example: Eddy gave Jimmy a wedgie in "If It Smells Like An Ed", and she yells at Ed and tells him that she is telling their mom. She should have yelled at Eddy because he was the one who gave him the wedgie, not Ed.
She gets a lot more love, trust, and attention from her mother than Ed who favors her over her son, sides her daughter and punishes Ed, and even gives her allowances instead of Ed. For example, Sarah sleeps upstairs in a warm cozy bedroom next to her parents’ room while Ed sleeps downstairs in the cold, dark basement.
Not only she is mean to the Eds, she is also mean to the cul-de-sac kids, and even her best friend, Jimmy once.
In "Boys will be Eds", she physically assaulted Rolf, despite him trying to to help Jimmy. She should whacked Victor the Goat with the tennis racket because he was the one chowing on the sandwich and his arm, not Rolf.
In "Thick as an Ed", She violently yells at Ed to wake him up to take her to Jimmy's house, when she could clearly do it herself (which she soon did so.)
Throughout the entire show, she almost never said anything positive about anyone in the show (other than Jimmy.)
To top this all off, since she never gets punished and gets away with whatever she says or does to the Eds, this makes her a complete Mary Sue to the point that Kevin and Jimmy are even more likable than she is!
Much like Kevin and Jimmy, she unfairly attacks the Eds most of the times. Even when one or two Eds did something wrong to her, she would beat up all 3 of them anyway.
Despite being young, her design makes her look like she's around the Eds' age.
She is never merciful.
She never learns a lesson.
She has a very awful design!
She has a much more innocent and sunnier side to her so long as she remains un-antagonized.
She has shown concern for Ed before, showing that she cares about him very deep down, one way or another.
She once feared Ed when he is a at her in Little Ed Blue.
She becomes kind to the Eds, especially to her own brother in Ed, Edd and Eddy’s Big Picture Show.
She cares a lot about, and is very nice to her best friend Jimmy, and they have a great friendship. Like she tried to stop Jimmy from fighting with Nazz in the episode "Key To My Ed", because Jimmy should know that he can't hit a girl. And in "If It Smells Like An Ed", Eddy gives Jimmy a wedgie that causes everyone except Sarah to laugh at Jimmy which pushes him to tears, and then Sarah gets angry and helps Jimmy, although she still had no right to threaten Ed that she's telling their Mom.
She got small comeuppances in "Fool On The Ed," "Sir Ed-a-Lot," and "Mission Ed-Possible", though this isn't enough to remove her from the Karma Houdini party.