Then you have heard lots of people being racist. That doesn't make it OK.
You are excusing her behaviour, which is pretty much the same as condoning it.
If a group of women are horrible to me on a night out, are you ok with me jumping to a barrage of sexist abuse? What if I was bullied by girls all through school, my last boss was a woman and made my life hell, and the woman who served me in the shop on my way to town was rude and obnoxious? (I'm a woman btw, just using a group I'm part of as an example for ease).
The right answer is no, just because you've had a bad experience with some women doesn't give you an excuse to insult the entire group, and that is what sexist language does.
The same with race. I don't care if every single Somali, Chinese, Māori, Phillipino, Pakistani (etc to incorporate every race on earth) person you have met has been horrible, you don't insult the entire group. And racial slurs never only insult the person they are directed at. They insult everyone who shares the same heritage. It's not something that can be excused (unless you genuinely think that some ethnicities are inherently bad or lesser than you, in which case, clearly you're racist yourself).
If there are issues linked to particular groups of people, we can address them without blaming or insulting the entire group. We can look at ways to combat sexual violence perpetrated by men, FGM, forced marriage, honour killings, drug addiction etc. We can acknowledge that there may be specific cultural norm/practices/beliefs or other factors (poverty, trauma, disenfranchisement etc.) that make them more of an issue within specific groups, and we can use this information to make positive changes. But this doesn't mean that we can walk around insulting and blaming entire groups of people for the actions of some.
Edited to add this is a reply to @Winlan81