There are many variations of that rumor.
I'm not sure anyone of them are true.
The most likely one is that one of Greta's handlers is related to the Rothchild family, but I take anything about the Rothchilds with a grain of salt. The vast majority of rumors are complete fabrications.
Personally, I think their power peaked in the late 1800's, and while they are still powerful, it's nothing like they were.
For instance, stuff about them "owning" the Federal Reserve is ridiculous.