You know, it’s really likely that what Rod said about the Reiss family and the coordinate isn’t just not true, but actually the opposite.

Eren could use it, but Rod skipped around the idea of Frieda being unable to. He said ~oh uh she just wasn’t experienced~, but if she ate her uncle, she should have all that knowledge. But she didn’t.

There’s a chance that Frieda couldn’t use it and the Reiss family had just been hording the power, trying to figure out how to use it.