I had a hard time understanding the leap she made near the end of her video yesterday about co moving frames. She summarized the time travel theory/paradox as it has been known until now, and then she made some kind of reference to an co moving inertial frame observer ("moving at the same rate as the average of all of the stuff in the universe" paraphrased) she claimed would exist under general relativity.
My understanding was that there was no such thing as inertial frame observers in GR, and that an observer in GR is actually something traveling on a world line in time with a future light cone and a post light cone. The observer portion in GR is literally the ability to observe with light, not a coordinate system as defined from within an inertial frame as in special relativity.
Thats because in GR, because of the curvature of space, you could not extend a coordinate system across all of existence because you knew that in some areas curvature would cause that to be not accurate. You can sort of declare space effectively flat within a local region but not across the entire universe.
It also wasn't clear what someone moving at an co-frame to the average of all the stuff in the universe has to do with faster than light travel - in a spacetime diagram a co-frame would be vertical with a horizontal constant offset, but faster than light travel would have to be in v > c zone not vertical. Maybe I'm too much of a layman to understand the logic she was using but none of it was very clear to me.