"No cause" does not mean "any cause". They can't fire you in retaliation. They can't fire you for being male/female. They can't fire you for being black/white/brown/pink/etc.
If they reply "For bad work perf", and it was really for poor work perf, they are fine.
If they reply "For bad work perf", and it really was because you were brown, and you prove it, lawsuit. It is obviously hard to prove. One way may be to show "Look I had 12 performance reviews, on all 12 I got perfect. In fact I did better on my perf reviews than people who are green, so obviously there is a bias for green people and against brown people.
Which as you see, the entire argument hinges around the exact reason you are fired. This is why when people are fired, it is safer from a legal standpoint to not give a reason. Even though that kind of sucks for self development. If you really were fired for being a jerk to coworkers... it may be nice to know that, so you can work on it at your next job.
Yup. It's also why references have gone from "so and so was an excellent/average/terrible worker" to "So and so worked here from xx/yy/zzzz to xx/yy/zzzz".
Usually, the answer is that companies would rather offer severance or settle than go into discovery if they fire someone for legal, bullshit reasons.
Companies don't want their reasons for firing people in the public. If they said they fired her for performance, she could subpoena not only her own performance history (Google has secret "calibration scores" that are not shared with the employee) but the ratings of others in the company and any HR actions taken toward them-- in order to find out if people were evaluated consistently.
No company wants its HR data in discovery, because almost every company has dirt. They'll usually settle.
