When the University of Florida softball team won the Women's College World Series on June 3, there was someone important missing: Heather Braswell.

The 17-year-old honorary team member died 10 weeks earlier of complications from brain cancer, but some believe she was there in spirit.

"In the outfield before the first game of the series, a yellow butterfly landed right on me," pitcher and first baseman Lauren Haeger, 21, a junior from Peoria, Arizona, tells PEOPLE. "I was like, 'Oh my gosh, that was Heather.' "

Heather's signature color was the yellowish gold of childhood cancer awareness, a cause she championed.

So the players wore yellow hair ties throughout the season and yellow elbow guards and sunflowers in their ponytails for the championship game. Heather's initials were emblazoned on their batting helmets.

"I know she was on the field with us," outfielder Bailey Castro, 21, a junior from Pembroke Pines, Florida, tells PEOPLE. "It was what gave us a great run."

Braswell, first diagnosed with brain cancer in early 2008 at age 11, became an honorary Florida Gator in 2009, thanks to the Friends of Jaclyn Foundation, which pairs pediatric cancer patients with high school and college teams.

Braswell fit in instantly, distributing Twizzlers to inspire rallies and handing out Team Heather bracelets. She even got her own locker in the Gators' clubhouse.

"She was basically a shy person, but we'd get to the field, and she'd run down the steps, hop the fence and go into the dugout with them right away," says her mother, Terri, 48, a nurse from Apopka, Florida.

Heather was cancer-free for more than five years, but in June 2013, doctors at St. Jude Children's Research Hospital in Memphis, Tennessee, found a recurrence of her brain tumor during a routine checkup.

With the team's support - including texts, messages and gifts from players and coaches each time she was in the hospital - Heather fought hard, but by January, her case was terminal.

Still, she found the strength to throw out the first pitch at the season-s home opener February 19.

"She was pretty sick at that point," says the team's catcher, sophomore Aubree Munro, 20 of Brea, California. "But she was so happy to be on the field and have that moment and feel that support. Our whole team just embraced her."

She died five weeks later, and after that, says Haeger, "We were playing for something bigger than ourselves."

Last week, with Heather's mom in attendance and her rally Twizzlers in the dugout, the team clinched its first-ever national title.

"Heather would have been excited beyond words," Terri says.