Having presented excellent revivals of Sean O’Casey’s three most important plays, the Irish Rep has turned to Little Gem, a new play by Elaine Murphy, that’s riskier. The play consists of three intertwined monologues. The structure may not appeal to everyone, and it’s a work that will find more resonance among women, but the performers, under the direction of Marc Atkinson Borrull, bring all their considerable power to invigorating a story that doesn’t rely on flash or action.