RE: Why was Kim Wexler so determined to fuck over Howard Hamlin?
Kim Wexler's motivation to undermine Howard Hamlin in "Better Call Saul" can be understood through a complex mix of personal dissatisfaction, ethical disillusionment, a desire to bring justice as she sees it, and her complicated relationship with Jimmy McGill/Saul Goodman.
Initially, Kim respects Howard and works hard to climb the ladder at HHM, the law firm where they both work. However, over time, she becomes disillusioned with the corporate law environment and the legal profession's impact on the lives of ordinary people. Howard, as the embodiment of HHM and by extension, the broken system that once refused to acknowledge Jimmy's talents and hard work, often becomes the target of her pent-up frustrations.
Moreover, she feels resentment towards Howard for his treatment of Jimmy after the latter's brother Chuck, a partner at HHMy commits suicide. Although Howard admits guilt and attempts to make peace, Kim feels he is doing too little too late. Additionally, her growing alignment with Jimmy's moral flexibility leads her to consider strategies she would have previously dismissed as unethical.
Kim's plan to harm Howard's reputation and his career by implicating him in a scandal is ultimately driven by a twisted logic that it will lead to a quicker settlement in the Sandpiper case, thus providing a substantial monetary award to the class action plaintiffs, who are elderly and in need of the settlement money. In her mind, the ends justify the means—a stark contrast to her earlier ethical stance.
She also seems to be seeking a rush or a challenge; for Kim, participating in Jimmy's cons and schemes becomes a thrill and an escape from what she views as a mundane or unfulfilling life.
Finally, Kim's plans against Howard can be seen as a key character development point, which not only affects the relationships within the show but also serves to highlight the potential corruption of a once morally-upright character, showcasing the complexity and depth of human motives and decisions. Her actions have far-reaching consequences, which are explored throughout the series.
In sum, Kim Wexler's motivations are multifaceted, and her actions are a combination of personal vendetta, quest for justice on her own terms, ethical compromise, and a search for identity separate from her legal career and relationship with Jimmy McGill.