US is by far it’s largest customer
That's true and there's also more to it.
The US is China's largest single trading partner but China has many many trading partners.
May nations now trade or at least negotiate in blocks. Both ASEAN and the UE, as blocks, do more trade with China than the US does. When it comes to individual nations the US isn't as far ahead as it might seem. Russia, Vietnam and Taiwan together trade more with China than the US does, despite having a combined GDP that's a tiny fraction of the US.
The key issue is that China has been working really hard to make itself less dependent on the US. They still have a way to go but they're much less vulnerable than they were a few years ago.
Is she really responsible for the problems of the US Green party?
As near as I can tell the EU Green parties had a different trajectory. They initially started winning seats in parliaments on purely environmental platforms. Those MPs actually started pushing green agendas in various parliaments. That, in turn led to more people voting for them. Eventually that had to adopt policy positions beyond the environment and they tended to be pretty left.
The US never had Green party members in a position where they could actually do anything useful about the environment. That means they could never fulfill their primary goal in the US. So when they tried to branch out the same way the EU Green parties did, they just turned into a vague hodgepodge of leftists ideas.
Is there any suggestion that Jill Stein's replacement would have any chance of saving the US Green party?