Throughout all her childhood, Susan has clearly always been the family favorite, being the pride and joy of Ida and Victor. She was the envy of Lois who learned to despise her. Susan was easily more talented and popular than Lois. She was often called on a lot of times by Ida whenever she needed help. In the first part of Baby, Susan had a brief misunderstanding with her mother that led her to move in with Lois for a while. Piama later had the idea to trick both Susan and Ida by telling Susan that Ida was dying and handing the phone to Ida to clear up the misunderstanding. At this point, Ida left the Wilkerson household to move back in with her favorite daughter. In "Lois' Sister," Susan gave Lois hell for being hopeless and untalented during her visit and it made her reflect on how unmotivated Reese was. It was also implied in Family Reunion that Susan is the reason why Hal's family along with Victor and Ida resented him for marrying Lois over her
Susan finally makes her first appearance in season 5 and despite being cordial to Malcolm, Reese, Dewey and Jamie and giving them presents, she was very bitter with Lois for years. This in turn lead to a huge fight between them when it's revealed that she still blames her for stealing Hal away from her and it led to her unmarried status. Susan also mentions to the boys that when she dated Hal, his family approved of her despite her lower background due to her being higher class and talented. She mentions Lois took the animosity too far when she stole Hal from her, causing the friction between their families and Ida blaming the latter for humiliating them. She admits to it and refuses to apologize for what she did because unlike Susan, she understood Hal better. When Lois learns that Susan is dying of kidney failure, she offers one to her. She initially refuses to take one of Lois' kidneys and states that she'd rather die. Susan also believes this is a pathetic attempt to get ahead of her because Lois still resented her for having their parents' favor. Lois pleads with her to accept one of her kidneys because despite their past problems, she still loves her. Susan ungratefully and begrudgingly takes one of the kidneys.
In Victor's Other Family, Susan was implied to have agreed to do the DNA test to help Ida's case and prove to Sylvia that she is Victor's common-law wife. Lois soon learned that not only that Victor wasn't her father and that he wasn't married to Ida, but also that Susan's DNA and blood type matched his. Thus revealing that she is Victor's only daughter with Ida.
Susan was mentioned in Season 6's Living Will, when Lois snapped Hal of his fake paralysis and told him he made the right decision to marry her over her sister. She was both families choice of wife for him because she was high class and talented.
Susan was mentioned in the last episode of the series Graduation, discussing with Lois on the phone cause she was not invited to the Malcolm's graduation; Lois says the her mother "bullied her" into giving her the last ticket they had for graduation (this possibly in order to see how Reese screwed up the graduation's ceremony with his prank). Although in actuality, she lied about this because she knew Susan had gave Ida her ticket so she doesn't have to attend Malcolm and Reese's graduation since she still blames Lois for foiling her chances at death.
- It was revealed in season 4's Garage Sale, Susan was more talented than her and was always encouraged to do better. She gave Lois a hard time about it and it was reflected on Reese(though it was later revealed that he doesn't care about being unmotivated and is almost just as greedy as Ida).
- In Season 5's Lois' Sister, it was revealed that Hal Wilkerson used to date Susan and that both families wanted him to marry her. However, he chose to marry Lois against their wishes and it lead to conflict between Lois and Susan for years.
- There are many references in "Lois' Sister" that are a homage to Metcalf's performance in wikipedia:Scream 2, Susan is crazy as her scream 2 character Debbie Loomis was (though much more insane). Lois mentions that her bully, Sidney Bower, was beaten up by Susan to protect Lois. Sidney is the name of scream's protagonist Sidney Prescott and Debbie Loomis did try to kill her.
- In Season 5's Victor's Secret Family, it's possible that Susan is Victor's daughter with Ida due to her DNA matching his and that she and Lois are half-sisters. It's also possible that she's eligible for his pension and may be related to Roberta.