A protest outside a New Jersey State Investment Council meeting last month in Trenton. : Michelle Perez, a former Toys “R” Us worker and single mother, used to have only a basic understanding of Wall Street. But she recently helped bring one of the world’s most powerful investment firms to heel. Ms. Perez, 28, from Vancouver, Wash., has been traveling the country, putting pressure on the private equity firm Kohlberg Kravis Roberts and the other former owners of the failed retailer to help the 30,000 workers who were laid off this summer with no severance pay.