People in the streets is probably what you need.
I didn't catch that one - is there a source? All I am Googling up is Trump telling her to chill, watch a movie, and a reference to anger management.
A global movement should be able to muster a better spokesperson than a child. No matter how earnest and scared a child may be, it is still a mistake to make major policy decisions on their say-so.
Yours is a standard attack line, because it allows you to pretend that it's only her saying this, and ignore all the thousands of others who've been saying similar things, from the IPCC to the Green Parties of the world.
A line of attack being standard doesn't make it bad. Putting forward a child to speak to world leaders and get worked up on behalf of other children isn't going to do the movement any favours. Greta is a puppet chosen because someone cynically thinks that putting a child on stage is going to tug on people's heartstrings. They might be right, but she doesn't have anything going for her that should command respect.
That does not make the flaws are irrelevant. She is being suggested as a leader but she is in no position to actually provide leadership.
Al Gore also had a long list of problems, but he was much more respectable than Greta.
We also need someone other than Greta as the face of it. While she does a great job, she's often dismissed due to her age and the US president has even publicly called her retarded in the literal sense.