How come Piano players always need sheet music? You know they practice these things a million times.
Actually, being something as bizarre (numerically) as a bass concerto, there's a really good chance she has never even seen the music or heard the thing before; pianists tend to know piano concertos by heart (for some strange reason), violinists know... etc. They might have just dragged her out of the bushes, said "here play this" and stuck the music in front of her. There is actually a quite steady and decent living to be made by being an "accompanist" for all the violin and flute and whatevers trying to become bigtime soloists. Or even studio and TV work, when so-and-so comes out on "Good Morning America" or "Ellen" and singes her big torchy ballad, you never notice the piano player. But there's a far higher likelihood that so-and-so is going to be singing in the subway next year while the piano player is quietly accompanying the Next Big Thing on "Good Morning America."
The ancillary* careers are a lot steadier than the aspiring "Next Big Thingies" for the most part. And it's fun to deride those people because they "can't improvise" or "play from the heart" but they're a lot closer to knowing how to do that than your average play-from-the-hearter is to doing what they do. The good ones don't even need to practice it up, just play the bugs on the page as-is.
*
(woo-hoo)