I had always understood it was Miranda's family (presumably her Zionist mother) who hadn't wanted her to have a part in the Christmas Play - Val Longstreet may have jumped to the conclusion that it would be impossible, but we don't actually hear the staff side of things. The Levy child, whose first name escapes me and I'm eating my supper so can't stop to look it up, isn't even allowed to go and watch, which Miranda is.