I work with an excellent doctor who is a tall, imposing man. But when he opens his mouth, out comes this soft, high-pitched voice that is so jarring because you don't expect that to come out of him. Certainly there is such a thing as voice coaches but I really don't think you can change it that much. About the only thing I could see her doing is try not to go up in pitch at the end of her sentences but that's hard to do when you have a certain way of talking that you've done probably most of your life.
I know I'm an uber fan but I did meet her in person and she's a lovely, gracious young woman.