Ask HN: Best way for someone to reach professors to get into a PhD Program?

My sister is trying to get into a PhD program. She has emailed about a dozen professors, and she's having a lot of trouble getting any of them to even respond back to her emails, let alone getting any information. Since most schools seem to require reaching out to a professor first, this has become a substantial blocker.

I was curious if anyone here who worked in academia knew of a better way to contact professors than just a random email for this kind of thing. Would it make sense to try and call them, or send a physical letter?

NOTE: Her location is the United States.