Patti Petersen Mirkovich (born December 2, 1954), formerly known as Patty Petersen, is a retired American actress.Petersen was born in Glendale, California, the youngest of three children. When her parents divorced in 1962, she and older brother Paul Petersen moved in with their mother, who later remarried. Paul Petersen costarred on ABC's The Donna Reed Show. Patty was written into the cast as Trisha, an adopted child after Shelley Fabares left the series.