Sara Tirschwell stood in the elevator of her apartment building, an elegant redbrick co-op a few blocks east of Central Park. She was headed to a law firm’s cocktail party, where she hoped one of the people in the room might spark the connection that would lead to her getting a job. This sort of networking event had once been the 54-year-old hedge-fund professional’s bread and butter, and she used to relish the thrill of working a room. But things were different now. Since the firing, there had been only bad days and really bad days.