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 has a very loud mouth, a hair-trigger temper, and is easily agitated by others, especially her brother. She is frequently seen with Jimmy and rushes to his aid the moment he calls for her. Sarah writes about her innermost feelings in her diary, and has a crush on Edd (though this is usually not quite enough to spare him from her wrath).
It's been shown that she shares her brother's superhuman strength, as demonstrated when she dropped a car on Nazz in "Truth or Ed." In "Little Ed Blue," she was apparently surprised to learn that her brother is much stronger than her, and is even more dangerous than she is when in a bad mood. Several minutes into the episode, she shouts at him, only to have him shout right back at her even more loudly and with more menace, which frightens her and makes her back off. She also seems to fear the Kankers, because unlike her brother, the sisters aren't afraid to bully the younger girl to get what they want. Eddy, who doesn't typically give in to Sarah as easily as Ed, often ends up being the one who provokes Sarah into physically attacking the Eds.
Sarah is Ed's pampered, loud and controlling younger sister who despises her older brother and his two good friends thoroughly, subjecting them to horrific verbal and physical abuse on a regular daily basis. She is very easily antagonized, particularly by Eddy's sassy remarks and insults, and has exhibited brute strength and extreme violence in reaction to the causes of her anger. Her softer, sweeter side is only visible when in the presence of friends, particularly her closest companion, Jimmy, whom she is seldom seen without, or when masking her supremely bratty behavior when trying to wheedle others into giving her what she wants.
Despite her severe animosity towards the Eds, she's noted for her infatuation with Edd, and this seldom can guard him from Sarah's harassment. Although it should be noted that Sarah's passion for Edd has faded from time to time, though there are many instances where she does seem romantically attached to him.
As mentioned previously, Sarah is only soothed by Jimmy's presence, and the two spend their days leisurely frolicking together and engaging in different childhood activities such as playing with stuffed toys and dolls. Due to her incredible lack of empathy and self-absorption, she is tricky to reason with, albeit few characters (particularly those notable for taming her) are able to bargain with Sarah, but when this happens it usually comes with a cost. Her intimidating and ferocious aggression has earned her the protection and respect of her older brother, Ed, who is fearful of Sarah.
Albeit she is hostile and antagonistic towards her bitter enemies, when in a less irritated state, a more childlike and innocent side to Sarah shines through; she joyfully partakes in tea parties, games of hopscotch, and pretend play alongside Jimmy and the other local children, and appears far sunnier and sweeter so long as she remains un-antagonized. However, she is normally seen with a disgruntled facial expression, and acts as a maternal figure towards the accident-prone, gentle, innocent, and fragile Jimmy, providing him with advice and discouraging him against the potentially-hurtful but seemingly fun and enjoyable schemes established by the Eds, or other cautions that could be lurking close by.