It's not that simple. Actors have a right to protect the use of their likeness in commercial projects like ads, and using a "soundalike" is not sufficient to say that isn't what you were trying to do. The relevant case law is Waits vs. Frito Lay. The fact that OpenAI approached her about using her voice twice and that Sam Altman tweeted about a movie she starred in makes her case much stronger than if they had just used a similar voice actor.