Shein aims to win over Wall Street and Washington In filing confidentially for an initial public offering, Shein, the ultrafast-fashion retailer, is showing ambition on two fronts. The company and its underwriters are betting that investors will be more receptive to I.P.O.s, even though high-profile market debuts this fall largely fizzled out. Shein is also testing whether it can endure what’s likely to be an increase in political heat on the China-founded e-commerce giant. The company has cut some of its most prominent ties to China, after drawing pushback from…