And the right to sue for redress of grievances is covered in the first amendment, for goodness sake. She didn't exercise it.
Good luck trying to sue one of the most powerful companies in history. I wouldn't dream of this.
Now, she probably wouldn't win, because there's no contract here and Google has no affirmative duty to host anyone's video in particular nor to pay them for it. But you can absolutely do it.
You can do it, but who has the resources (especially the motivation and willpower) to drag such a case through the various appeal instances, with the issue that if you do lose, you have to pay the opposite party's lawyer bills? No way in hell I'd risk loading up THAT debt risk.
Edit: I meant if anyone thinks they should depend on youtube ads for income, they are delusional.
Exactly this safety net is what the "gig economy" tries to cut...
Or, even better: as here the case seems to be that the shooter depended on Youtube as income, why shouldn't she have the right to have her effective "firing" appealed in a proper court of law, like in Germany?