Look at the dates, the evidence dates back to 2012 and December 2015, well before she was even within the public eye, it can't have been statements meant to troll attention she wasn't getting yet.
Honestly you can look at the reasons for her being fired in three, separate ways.
She could've gotten fired for the child abuse stuff, look, if someone is a pedo and doesn't actually ACT on this impulses I don't really care, it's a mental defect due to an error within the wirings of the brain, it's something alot of them can't actually control. Not acting on them is the important thing. And then if you're crossing the line trying to advocate for the legality of that shit, and then ALSO working at a company that designs products for children? It gets kind of sketchy.
She could've gotten fired for just the general inflammatory nature she was having on twitter. That's a very common thing. It doesn't matter if you put "These opinions do not reflect [parent company]" on your bio, banner, avatar, whatever, because they very much DO. If an artist at Rare Studios(Is it software or studios?) or something started going "I HATE BLACK PEOPLE" or other inflammatory shit on his twitter do you really not think that wouldn't reflect badly on the company? Whether you like it or not, when you're working for a company, and you have a profile somewhere that is specifically with your name and lists your company name, anything you say or do reflects on that company. It is the internet though, you can easily make a separate profile to do whatever you do. Companies care if Bill from [company] does something bad, companies don't really give a shit if Buttlord59 does anything though.
And finally the reasons we were given by Nintendo, the modelling. Which on the base level sounds innocuous, but you also have to remember Nintendo is a child orientated company, irregardless of what a good amount of their actual audience is, Nintendo's focus is children entertainment. As a result, someone doing the very particular type of modelling she was doing, was bad for their image. Especially when it involves their products or something you probably don't want your child looking at. This isn't the first time that similar firings have happened because these type of things mess with their branding, Disney is actually fairly notorious for this, basically if you worked for Disney and had a public profile, you wouldn't be able to get away with half the shit she did, let alone if you were one of the 'face' actors. It's simply a harsh reality of working for child friendly companies.
Or... she got fired because some people on the Internet said bad things about her. I mean, I guess? If Nintendo was going on that though you'd think Treehouse as a whole would've been shut down.