Sopper was in the process of moving to California for the chance of a lifetime.
A standout high school gymnast at Fremd High School in Palatine, Sopper earned a gymnastics scholarship at Iowa State. After college, she coached part-time while becoming a lawyer.
Eventually, she served in the Navy's law division, the Judge Advocate General's (JAG) corps. However, she did not give up her passion.
"Her love was always gymnastics," said Kminek.
When she found out the University of California Santa Barbara needed a coach a month before school started, she knew it was her chance and applied.
"It was her dream job; she always wanted to be a women's head gymnastics - collegiate gymnastics - coach," said Kminek. "She interviewed over the phone and got the job, and that's why she was on the plane - moving there."
"The minute I heard it was a flight from Dulles to L.A. that had left at eight in the morning, I don't know, I just knew," said Kminek.
Sopper was one of the 59 people on American Airlines Flight 77 the morning of 9/11 when it slammed into the Pentagon.
"I just broke down and said, 'I can't do this, I can't do this,'" said Kminek. "But on the other hand, you have to do this. What are you going to do?"
Ten years after the 9/11 attacks, a somber memorial stands at the Pentagon, honoring those who were killed when the plane hit the headquarters for the American military. The memorial is filled with silver metal and stone benches marked with the names of the dead.
The Pentagon was one of two targets hit on 9/11, the other being the World Trade Center in New York City, both towers of which collapsed after each was hit by a hijacked commuter plane. Another plane, United Flight 93, crashed in a field in Pennsylvania after passengers attacked the hijackers who had taken control of it.
Three people from the Chicago area died in the attack on the Pentagon: Sopper, Naval Lieutenant Commander Patrick Murphy from Flossmoor, and Naval Commander Dan Shanower from Naperville.
Murphy and Shanower were at work in the Pentagon when the plane struck, so the names on their benches can be read while facing the building's western wall. Mari-Rae Sopper's name, like the names of all of the victims who were on the plane, faces the sky.
"We still miss her and wish it didn't have to be that way, but there's an acceptance that comes," said Kminek.
Ten years later, Kminek says she still misses her daughter, but she's comforted knowing Mari-Rae lived her life to the fullest.
"She lived her life basically like she wasn't going to be here tomorrow," said Kminek. "If she believed in something, she went all the way, and I think if more people did that, they'd be happier,"
Sopper's family plans to travel to Washington, D.C. for the 10th anniversary of the attacks. They have established a fund in her name that supports women's gymnastics.