And so it goes in Vichet Chum’s new play, “Bald Sisters” at the Steppenwolf Theatre Company, an identity play that looks at two immigrant women with familial origins in Cambodia, both trying to reconcile their traumatic heritage with their current lives and beating each other up emotionally in the process. Chum’s play, which had its world premiere Sunday night in Steppenwolf’s new, in-the-round theater under the direction of Jesca Prudencio, is a very weighted play. One of the most interesting aspects of this particular play is how the older sister lived through a different history, seeing things that escaped her younger sister’s memory.