Do we know this didn't happen, out are we just assuming?
There's a lot of assumptions all around. We still have no confirmation of what the second job is, just simply that there are risque photos around with her posing with her company's products, and accompanying links to an Amazon wish list of various items.
The key issue right now is we don't know 100% whether or not the "second job" is related to the risque photos. We do know she used a pseudonym for it, and some extrapolate that to mean that if she went that far to not show her name, she wouldn't dare mention it on the main Twitter account, like posting photos. But photos were posted, but with no real explanation about their origin or purpose. So there's disagreement over if there is that link or not.
Originally when this all happened, she didn't elaborate on the reasons for being fired, letting followers fill in the blanks, and minds ran wild. Once Nintendo offered their reasoning, she elaborated, also murking the discussion a bit conflating "second jobs aren't allowed" with "second jobs that conflict with the company aren't allowed", but still defends that holding an outside job is allowed, but she didn't elaborate on the nature of it.
So it seems right now a lot of the discussion is being fueled by assumptions.
Ultimately, my opinion is that she was unfairly targeted, but they did find a fire-able offense, so that's why they took that action.
Risque photos on their own are fine, but when they involve the products that you represent during your day job that's where the conflict of interest comes in, sending VERY mixed messages. If Nintendo chose not to act, then it would appear they endorse such behavior by omission of action. And that is making the assumption it relates to her second job.
We also must keep in mind that she's been warned by her bosses about her public persona on multiple occasions before anybody started targeting her. (Unless GG started harassing her back in 2014.) So instead of treading lightly, she kept on being herself, discussing what she believes in.
Building on that, the discussion about Nintendo's reaction to it hinges on whether this was the last straw for her or not. If they had done a "please take these posts down" request or "please leave your other job" statement before letting her go, that would probably ease this discussion a lot, but neither party is stating that.