I'll ask the devil's advocate / contrarian question: How big a slice of the human voice space does Scarlett lay a claim to?
The evidence would be in her favor in a civil court case. OTOH, a less famous woman's claim that any given synthesized voice sounds like hers would probably fail.
Contrast this with copyrighted fiction. That space is dimensionally much bigger. If you're not deliberately trying to copy some work, it's very unlikely that you'll get in trouble accidentally.
The closest comparison is the Marvin Gaye estate's case. Arguably, the estate laid claim to a large fraction of what is otherwise a dimensionally large space. https://en.wikipedia.org/wiki/Pharrell_Williams_v._Bridgepor...
Are companies better off not even trying to negotiate to begin with?
What I wouldn't do is use anything that remotely sounds famous. And I would definitely not use someone that said "no thanks" beforehand. And I would under no circumstances send emails or messages suggesting staff create a voice that sounds like someone famous. Then, and only then, would I feel safe in marketing a fake voice.
Consider the hypothetical: EvilAI, Inc. would secretly like to piggyback on the success of Her. They hire Nancy Schmo for their training samples. Nancy just happens to sound mostly like Scarlett.
No previous negotiations, no evidence of intentions. Just a "coincidental" voice doppelganger.
Does Scarlett own her own voice more than Nancy owns hers?
Put another way: if you happen to look like Elvis, you're not impersonating him unless you also wear a wig and jumpsuit. And the human look-space is arguably much bigger than the voice-space.