Even with a belly full of beer and benzos at age 18, I dry heaved before getting on stage. It was virtually impossible for me to perform without that added help. When I quit all drugs and alcohol 5 years later, I quit music completely. My stage fright by that time had turned into full blown agoraphobia, and I needed lots of help. Thankfully, it was 1984, and the help offered me was of a holistic nature as opposed to medication. I was told, by psychiatrists at that time, that medication would only mask the anxiety and work as a Bandaide.
It took me 2 years of therapy and practice with other tools before I could function well enough to take a course in college, and after doing that successfully I decided to take an acting class to maybe help overcome my fears. The 2nd day of class our professor gave a speech about stage fright that floored me. It was as if he were talking directly to me.
He started by mentioning the fact that Sir Lawrence Olivier at times had to be pushed onto the stage in order to get him to perform. He noted lots of other actors and musicians who suffered horribly from stage fright, letting us know that we were at least in good company. Then he went on telling us how so long as we didn't make anxiety and fear the enemy, we could actually make it work to our benefit. With practice we can take that energy, and channel it into our performances. He said a lot more, but I want to keep this post short. I became determined, and I found he was right.
I wound up acting in a few shows that year, and then carrying over what I learned to music.
The anxiety never completely went away, but it at first became manageable... and then at a certain point, enjoyable.
In short - this CAN be worked with, or overcome, but as others have said repeatedly...
She needs to WANT to get better. Its not going to "just happen."
One of the things that really motivated me that the professor talked about, that I didn't mention, was the idea of stage presence. He said that we'll often find that the people with the MOST stage presence, are also the ones most terrified to be on stage. They just learned how to channel that energy into something much more positive. I found that to be true.
Last note: Not long ago I saw a clip of Miley Cyrus that I can't find again, dammit

. She was about to walk out on stage, was shaking and openly admitted to being terrified. She said, "Yeah... I know, you're Miley Cyrus and you're scared??? Crap yeah!!!"
It works for her.