Right now it looks like SendGrid fired her because of the DDoS they suffered a few hours ago. Once you can blackmail a company into firing someone like this .... I think it's dangerous for the company.
Do you have evidence for this? If it were me, I'd fire her because she caused a huge wave of negativity toward the company. I don't know what an "evangelist" does, but I'm pretty sure this is the opposite of it.
I'm not saying they weren't right in doing so, but it looks like they cave to blackmail.
I'm sorry, but there is zero reason to believe this over other plausible explanations given in this thread.
I'd have fired her, too.