But the next four years changed everything, she says -- because of softball.
"My high school experience was OK academically, but my confidence came from sports," she says.
So when Diglio moved from being a big fish on her high school softball team to a small fish in the big pond at CMU, "my confidence was shattered," she recalls.
The first two years on the Central team, she barely played.
"So I had to learn tenacity," she says. "I learned you have to work hard to get what you want. I had to dig in my heels and work hard every day."
That -- and so many other lessons -- remain with Diglio today as she heads the 2,000-student Novi High School as principal.
"Everything I do daily, I use the skills I learned in softball at Central," says Diglio, 46.
By her senior year, she was a starter. But along the way, she realized everybody is important -- not just the starters.
"I learned everybody has a role, and you have to live that role with pride and dignity and accept it," she says. "That you're not always going to be on the top of the pyramid, but you're there to support others.
"I could have gone to another school and played more," she says. "But I picked Central's program because it was a success. We won two MAC championships when I was there. At one point, we were fifth in the nation."
When Diglio reflects on her time at CMU, she doesn't separate her academic experience from her athletic career.
"Softball was as big a force for me in college as the academic piece," Diglio says. "The structure. Discipline. Accountability. Learning to be on time. All of that shaped me to be a better student, and a better person."
Behind all of those lessons was her coach, Margo Jonker, who had high expectations, Diglio says.
"Margo held people accountable," she says. "I use that skill a lot. I'm hard on kids, in terms of holding them accountable. Right down to their behavior in the stands. I tell them to be positive, always. You're representing yourself, your family, your school. That goes right back to Margo. With her it was family first, then school and team. And she was never negative.
"She taught us to be better than we were," Diglio says. "I'm so grateful for that, and I still tell Margo that, 25 years later."
Diglio graduated in 1989 after majoring in health. She went on to teach for 14 years and has been in administration for a decade. Being part of a team taught Diglio skills that are critical to her work now, she says, as a high school principal.
"I had a union meeting this morning and teamwork was our topic of conversation," Diglio says. "What can we do as a team in our roles as educators?
"I'm so lucky to be where I am," she says. "There's no doubt I am who I am because I had those opportunities at Central. Success breeds success."