It seems to me there are two possibilities. Either she made them up at the time, which people have been known to do, or it actually happened.
On the subject of Larry King and the phone call, you don't even need some expert voice matcher. Lot's of people knew the woman's mother, and lots of people can recognize voices. Proving it was her mother, or disproving it, is very, very, easy. I'm pretty sure it was her mother.
Now, another witness corroborates that she told the story back then.
So, one thing that has been known to occur is that someone isn't doing a great job and is either thrown out or decides to leave and instead of telling family and friends, "I'm doing a lousy job at work. I need to get out before they fire me." she says, "I was assaulted", or "It was racism" or "My boss was abusive" or....fill in the blank with something that doesn't make it your fault. I haven't followed the story so I don't even know if it's a possibility.
Another option is that it actually happened.
An awful lot of people are going to believe the latter, even if it can't be proven.
For my part, I will still vote for him, and I don't even particularly care if it's true. Trump has done just as bad. I generally like Biden's politics. And, I really don't like going into 30 year old personal stories. I said that about Kavanaugh. I'll say it about Biden. At some point, I'm ok with an informal "statute of limitations" on personal conduct. Maybe that makes me a bad person. However, I would be more comfortable with a different candidate, for this and other reasons.