For an undergraduate degree, BYU is great.

Also, assuming this is about the 102 ranking on US News, keep in mind that the graduate programs are a big factor in those rankings. Getting an undergrad degree is different than a graduate degree.  And at some schools, teaching undergraduate students is seen as a burden to many professors. They care more about their research. You may have a better undergraduate experience at a place that cares more about teaching undergraduates.

Based on my post graduate schooling with engineers coming from many universities listed in the top 30, BYU is not lacking. My BYU ChemE peers were just as bright as those coming from those other schools.  I was just as prepared.

She will find many equally brilliant people at BYU, and she will be challenged. And if she wants to pursue an advanced degree, she can decide the school later. A BYU undergraduate degree will be a great stepping stone.

However with all that being said, BYU isn't the only place to get a great education or to grow spiritually. She'll have to figure out what's best for her. But she shouldn't let that ranking be a deterrent, nor should pride and her wanting to feel prestigious be a factor.