So basically she's accusing China of having "industrial overcapacity", that is to say their production is supposedly higher than the demand.

Arnaud Bertrand wrote a great article on this.

TL;DR: The 3 main signs of overcapacity (capacity utilization rates, inventory levels, and profit margins) for China are all at similar rates as the US, indicating they are not in overcapacity. And they aren't even selling them at a lower price abroad than at home to beat competition; it's the opposite. He concludes that China is simply getting too efficient at manufacturing these days and the US is starting to struggle to compete with that, and this is just them trying to convince China to slow down.