I can almost gurantee this was not the reason she was fired. If you have a good employee who breaks the rules you council them. You don’t fire them. If you have a bad employee who breaks the rules you document it and fire them. (In my case I had to council them, put a letter in their file, then, if “it” continued we’d develop and sign an improvement plan. Only then, when the activity in question continued, could I fire them. I would always call them in, pull out the signed plan and ask if they’d complied. “Well, no but...” No but’s. Did you or didn’t you? Then I’d ask what action I had to take. They’d reluctantly say “fire me.” I’d say how sorry I was but would you please come with me. Oddly, they always acted elated when I fired them. Without exception. Weird.)
My first wife and her boss kept putting off talking to and working to terminate an employee who broke all kinds of rules, was tardy, left early and took over long lunch breaks, etc. One day she came in and declared that she had cancer. I told my wife “you can’t fire her now, that’ll look like discrimination and retaliation.” That woman had a guaranteed job from then on.