Catalysis of the reaction: 3-hydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione + FMNH2 + O2 = 3,4-dihydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione + FMN + H2O.
3-hydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione monooxygenase activity