Transmission or timing [or something else?]

My daughters car jerks periodically at highway speed. She’s been told her transmission is OK and she’s not concerned about the car. My wife is very concerned! It has never stalled, and seems to run fine, then a little rough [unless I imagine that] and then jerk, jerk, jerk, and then fine again.
She drives an '07 Ford Focus.

Is the ignition timing on this engine even adjustable?
Somehow, I doubt that it is adjustable.

Instead of looking at a timing problem or a transmission problem, my question would be:
When was the fuel filter last changed?

If the answer is “never”, “I don’t know”, or “more than 3 years ago”, replacing the fuel filter would be the first thing that I would suggest for you to do.

And I might ask, “when were the spark plugs or wires changed”?

Yeah, +1 on the spark plugs and wires.

I had a very similar problem with a 2002 Chevy Malibu. I’d changed the spark plugs out to Bosch Platinums a while back, and thought I’d done my engine a favor. However, after I experienced the same “jerking” you describe, my mechanic changed the spark plugs back to OEM ones. Car ran like new after that.

Good luck.