Mary Louise Diffendal

Mary Louise “Mary Lou” Diffendal, age 92, of Robinson Township, passed peacefully on to eternal life on Saturday, January 24, 2026, surrounded by her adoring family. Born on November 17, 1933, in Hays, PA, she was the daughter of the late Mathilda and Matthias Miller. She was the beloved sister of Donald Miller and the late Mathias “Bud” Miller, John Miller, and Catherine Shuster.

Mary Lou was a 1951 graduate of Taylor Allderdice High School and began her career as a secretary with Westinghouse Bettis, later advancing to the corporate headquarters in Pittsburgh. In 1961, she married the love of her life, the late Thomas S. Diffendal. Together they made their home in Robinson Township in 1967, where they raised their four sons and built a life rooted in family, faith, and hard work.

In 1974, Mary Lou and Tom founded American Vending and Food Services, which grew to become Laurel Food Systems; a business they built together with pride and dedication.

A devout Catholic, Mary Lou was a longtime member of Holy Trinity Catholic Church (Archangel Gabriel Parish) and served faithfully on the Bereavement Committee and the Ladies Guild. She was also active in several organizations, including AARP and Silver Sneakers.

She found joy in caring for her immaculate, country-club-like lawn and gardens, and above all, in the lives of her children and grandchildren.

Her sons recall their mother being an avid baseball fan who took the streetcar from Hays to Forbes Field to watch the Pirates play. In 1960, she brought a baseball to the park, and over multiple games had it signed by every member of the Pirates’ World Series Team. A decade later, her two oldest sons took the ball outside to play with it and, in the process, accidently destroyed what had been one of her prized possessions – an incident that became a family story retold, eventually, with affection and humor.

In 1972, she surprised her husband—an avid Steelers fan—by purchasing season tickets, something he had always wanted but never felt justified spending the money on. That gift began a tradition that lasted for the next 40 years, as they attended Steelers games together season after season.

She is survived by her loving sons: Tom, Don (Linda), Rick (Rene), and Dave (Laura); and her cherished grandchildren: Tom, Theresa (Micala), Rachel (Kevin), Sherine, Anjelica, Ben, Ethan (Mara), and Eric.

In lieu of flowers, the family requests donations to be made to EWTN in Mary Lou’s memory.

Friends and family will be welcomed at William Slater II Funeral Service, 1650 Greentree Road, Pittsburgh (412-563-2800), on Friday, January 30 from 2:00 – 4:00 pm and 6:00 to 8:00 pm. A Mass of Christian Burial will be held on Saturday, January 31 at 10:00 am at Archangel Gabriel Parish/Holy Trinity Catholic Church, 5718 Steubenville Pike, Robinson. Interment to follow at Resurrection Cemetery.