According to immigration lawyers, it is very hard to get docs through O-1. You literally have to be international star. She is not, but still, she is level above what many musicians achieve in their lifetime.
I've heard of people getting O-1 while being far less than an "international star". Canadian founders getting minor acquihire buyouts have gotten them. You just need to get some letters from influential people. ie, business leaders in the local industry or a politician. Like most things it's as much about who you know and how well you check the right checkboxes as it is about merit. This another perk of VCs and selling to big companies.
My understanding the same as that of my two sibling comments. You just need to demonstrate excellence in your field in order to get an O-1. For example in Computer Science, that might be X citations in published work, Y reviews you've written as reviewer (counts as service), and letters of support from experts in the subfield of Computer Science. If your pianist friend has won international competitions, CD recordings and performed with orchestras around the world, that surely counts as excellence in her field. She should consult an immigration attorney ASAP. Even if initial consultation costs money (and it often doesn't), it sounds like a worthwhile path forward if she wants to stay. O-1 is not as prestigious or rare as you make it seem.
It really depends on the immigration lawyer, I know many people who study public health & even computer science use O-1 as alternative. non of them are even close to have international influence