Consider if the situations were reversed. What if some white male engineer was simply being terse in an email to her. Might she attribute it to rudeness, sexism, or transphobia? If the company fired the engineer would you be arguing that she should be a bit more charitable in her interpretations?
It can be very hard to capture the subtleties of spoken word in text form. The onus has pretty much always been on the individual to ensure they are being professional. I definitely think something is fishy here. It may very well be that Github has some serious issues, but the flip side of that coin (and Occam's razor) is that she sent out some rude emails and was fired.