I deeply regret that Joni does not know how to write sheet music. The 'loss' in Joni's inability to write is she cannot be the creator behind the orchestral music of her last and next project. She has to rely on someone else arranging the music, which removes it, for me, a bit away from being HER music and it becoming someone elses. She has managed to work around this shortcoming quite beautifully. It's certainly hasn't hindered her composing on piano or guitar. When she's needed to, she hums the parts. That seems to work well enough. I guess if you surround yourself with masterful players, the weakness kind of fade off into the back ground.
Joni is a wonderful composer. It's a shame she never learned to put it on a page.