It doesn't matter that what she says is a lie?
It's interesting how you twist yourself into a pretzel (you "probably", maybe, a little bit, think that what she says about the sponsor is a lie) to end up with the conclusion that her actions are somehow justified and the board is committing some terrible crime of censorship.
The validity of her complains is very much the core of the issue.
She only gave one example (that Google is "involved in corporate mass surveillance") and presumably that is in context of NSA spying and the consensus around that is that it's a lie.
At her level badmouthing a partner is grossly nonprofessional. Spreading vicious lies - that's a no brainer reason to fire her.
Also, let's not be naive about the context of her complaints. When she says "when someone asks me..." she (or the board) doesn't mean "my college friend at a dinner party" but "a member of the press".
And given the state of journalism, "the member of the press" is not interested in Linda's perspective on Google's spying because she has literally nothing new to add.
In that context the only value for the press is to reduce her views to a click-baiting headline of "Code Club board member accuses sponsor Google of mass surveillance" which would damage Google precisely because they were nice enough to sponsor Code Club.
If she complained about AT&T (which actually did illegally spy on Americans in massive constitutional violation, for which they received a retroactive immunity), there would be no story because AT&T is not a Code Club sponsor or Linda doesn't feel like complaining about AT&T.
I'm not privy to the details but the simplest interpretation of what we know is that she was hell bent on spouting nonsense of the "Google mass surveillance" kind to the press and the board was very justified in worrying about a press creating a mountain out of a molehill to the point they felt they had to intervene.
So far there is 0 evidence that Linda had some novel complaints that are serious enough to risk damaging an organization that helps kids learn to code. So far all I see a selfish, self-righteous individual.