As Ms. Tirschwell sat there processing the news, the chief executive of TCW, David Lippman, walked into the room. The company would offer her a severance package of $500,000 if she signed an agreement promising not to sue. “Look at me,” she recalled Mr. Lippman saying, according to a court filing. “This is not negotiable.”

Ms. Tirschwell left the meeting without accepting the offer. This wasn’t actually about compliance, she believed. It was retaliation. Because there was an entirely different narrative that Ms. Tirschwell thought explained why TCW was so eager to get rid of her: Just nine days earlier, she had made a formal complaint of sexual harassment.

On Dec. 5, Ms. Tirschwell had written TCW’s head of human resources to complain that her boss, Jess Ravich, had pressured her into sex several times during her tenure with the firm. When she stopped sleeping with Mr. Ravich, she claimed, he stopped supporting her fund, making it impossible for her to succeed at her job. The day after receiving her complaint, the human resources head and general counsel interviewed Ms. Tirschwell and promised to investigate. But then came her firing.