A Cardinal O'Hara High graduate, then Theresa Shank, she was the star of that Mighty Macs group in the '70s, in the pantheon of talent this area has produced.
She went on to win a national title as Rutgers' coach, and coached the U.S. Olympic women's hoop team in Barcelona. All by the time she was 40. She was inducted into the Women's Basketball Hall of Fame before she hit 50.
At age 62 - "a young 62!" - she isn't looking for a team. Five teenagers, four girls and a boy, had her fully engaged for the afternoon.
"When I'm on the floor, nothing hurts," Grentz said as the players took a quick hydration break. "When I walk out of the gym, everything hurts."
The players in front of her had skills. Nicole Munger made all-state as a junior last season at Central Bucks West and already has committed to Michigan. Her most noticeable trait: You could put a ruler across her shoulders as she squared up for every shot, whether a step-back 10-footer, a three-pointer off a double-crossover or a spin move off a short rebound.
Grentz had Munger and the others working on that double-crossover move followed by a jumper.
"It's got to be quicker, got to be quicker," Grentz said as the drill began. If the shot missed, Grentz wanted a putback.
"Because the defense is invariably . . ."
She looked to Munger to finish the sentence.
"Lazy," Munger said.
Most of the drills, whether for shooting or passing, were done with the players dribbling two balls at the same time.
"What I'm trying to do is tell the right side of the body to do one thing while the left side is doing something else," Grentz said, comparing it to juggling.
Her background is like a highlight reel of the rise of women's basketball over the last half-century. Growing up in Glenolden, Delaware County, Grentz remembered how a number of neighborhood boys got together for a catch with a dad, who wouldn't throw it her way, explaining that he couldn't, she was a girl. She tells that one when asked about the biggest hurdle of her life.
If that was a prevailing hurdle of the time, it was cleared. (In her new book, Lessons Learned from Playing a Child's Game, written with Dick Weiss and Joan Williamson, Grentz notes her own father put up a rim in the driveway for her.) She found role models on the 76ers but also a library book on Babe Didrikson Zaharias, opening her eyes to possibilities.
She led O'Hara to several Catholic League titles, enrolled at Immaculata, sometimes hitchhiked to get there as a commuter, before the Mighty Macs turned into a Cinderella story worthy of Hollywood, winning three national titles, as Shank became a three-time all-American and also national player of the year.
Right after graduation, while teaching sixth grade at Our Lady of Fatima School in Secane, she coached St. Joseph's for a couple of years before moving on to Rutgers, becoming the first full-time women's coach in the country. Then she coached a dozen years at Illinois.
Asked about coaching highlights, Grentz said: "Coaching was always like a business. There were wins and losses. You tried not to get too high or too low."
That perspective was hard-earned. Coaching the Olympic team was a career highlight, but losing a semifinal, settling for bronze, she had to get past that. She wrote in the book how for years afterward she couldn't go past a bookstore without buying a self-help book.
Outside her gym now, her convertible has no identifying personal adornments except two words around the license plate: "Immaculata Alumni."
Inside, the workout breaks were usually just long enough for a couple of swigs of water. Hydration wasn't part of the landscape when Grentz played or much when she coached, she said, but she's on board with it. She just believes that practice time is meant for practice.
"You want to stay on the bench, stay there," Grentz said. Even now, she said, she's not the type to sit on the side drinking a Coke.
She believes this skill-development work suits her: "I don't have a dog in the fight. . . . I don't have to worry about them transferring. I can tell them the truth."