That's so exciting! Yes, it is perfectly fine to attend your niece's glistening. As you know, men sweat, women perspire, but ladies glisten. You should be very proud your niece earned a spot in the soccer camp at the University of Portland. It's a prestigious organization. The women's team won national championships in 2002 and 2005 and past teams include seven Olympian medal winners—including five who competed twice!
It's true that UP is affiliated with the Catholic Congregation of Holy Cross, but I can affirm it is possible to attend events—and even get a degree—without having to engage in any Catholic practices. It's where I went, in fact. Although one of my favorite teachers was a nun (Sister Angela Hoffman did significant research on the cancer drug Taxol), and I had a math class taught by a Catholic priest, I think my church history professor was Episcopalian. I can't imagine my hippie physics instructor—let alone my Iranian statics and dynamics professor, my Indian fluids teacher, or my dear Pakistani dean—were Catholic.
Engineering, as soccer, knows no religion.
So, feel free to watch your niece play soccer. There will be no incense, prayers to Mary, or eucharist served. Honestly, even if it were her
christening, it would be okay to attend.