I play a little game when running.

If I hear a car coming up behind me, I pick a point farther down the road and try to get there before the car passes me. If I manage to do it, I pick another spot.

It's not hard for me to imagine changing the game a little and make my goal to pass a bike struggling up a hill. I've probably done it.

So it may not be that she always runs that fast up hill. On the other hand, 6 mph is only a 10 minute mile, - which is pretty slow for a runner.

Sorry.

Edit: If she turned around it's possible she was doing some hill work and she was pushing herself pretty hard.