What if she wasn't doing her own voice? Many actors have voiced characters not in their own voice over the years. Does Elmo's original voice actor own Elmo's voice or is it whoever owns Sesame Street?
I'm not necessarily making any assertions, I'm genuinely asking cause I don't know what kind of precedent is here. Though personally I'm not convinced of the case against OpenAI, other than bad optics from Altman.