“Mirror Dance” puts a human face on the impact of Cold War politics with a touching profile of Cuban ballerinas Margarita and Ramona de Saá, twin sisters who became estranged after Margarita left her home permanently for the U.S. in 1964. Margarita, who joined the Pennsylvania Ballet Company before opening her own company, is shown in a heart-wrenching reunion with her sister in Havana's airport, her first trip back to Cuba in nearly 40 years.