I would consider helping her look into what goes into school rankings and then also having her examine what she wants to get out of her undergrad experience. (And maybe BYU might not actually be the answer and that can be OK).

My opinion is that BYU is a great place to get an undergrad degree that will get you into a quality graduate program. Indeed other universities can also do this, but BYU is not lacking.

In my field (math), I got both my BS and MS from BYU. I then was admitted to some very quality schools for my PhD. BYU's math department is not highly ranked. But my work still stood for itself and I was fine.