That's a daft thing to say, for one thing i'm white so she's not going to be harassing me racially.
She could be racist for all sorts of reasons: upbringing, environment, what she's heard in the media or church or whatever. What you have done is really rather dangerous: you are assuming that racism iss imply the product of mental health problems or even just stress. This undermines just how pernicious and evil racism is. It's arrogant and dismissive and unwittingly implies that people with mental health issues are racist as well. I think you need to rethink what you've said.
I'm more concerned with racism from people like Nigel Farrage and that nice Le Pen woman he's chummy with, than one random angry woman on youtube. Clearly the driver didn't think she was much of a threat or he would have calld the cops, no question.