4 years is a long time for someone who's a racist to go without being flagged/documented by HR for a comment.
I'd argue that firing her without at least attempting to remedy why her ideas or thoughts are wrong is unethical. She's in her 50s and she should understand how much the world has changed from 1980s to 2014. "jive" doesn't even exist anymore.
HR's job in itself is to help the business achieve it's goals by managing the finite labor and resources humans offer in the workplace.
http://en.wikipedia.org/wiki/Human_resource_management
HR has failed to teach diversity and inclusion in this respect. HR has failed if it can't teach this woman why her thoughts about her personal opinion on who her daughter dates isn't a proper thing to express in the workplace, nor why it's wholly wrong to think that way.
This change happened because the Federal government stepped in and actively undermined what State and local munis were doing, which was protecting civil workers who're bigots and KKK members in the South. They were protected just by being involved in government. That change is a great one. It was the one our country needed. Calling in the National Guard to protect black students during integration was needed.
This is a woman, who honestly sounds like she shouldn't have been in that workplace to be with, talking about who her daughter can date and can't date. Who the fuck thinks that is something okay to talk about at work?
That's why HR exists! To protect those who don't have authoritative power & to defend the business from an abusive boss or bigot co-worker. HR is failing in this instance.
If HR doesn't do shit(Which is what those people who're paid in HR to do), then the company fails to operate properly and then fuck it, fire her. A company that doesn't have the bare minimum of HR procedures established doesn't garner much sympathy from me.