Do what works for you. If the 'abs first thing in the morning' fits your schedule and is working, keep it up.
I think there are several reasons Cathe and most other instructors put abs last: primarily that they use a smaller amount of muscle, so you don't have to have a lot of energy to do them, like you would to do squats, for example; and that they are done on the floor, and ending the workout on the floor, then going into the stretch, makes for a better flow.
Some workouts, like "The Abs Diet" workout, do start with ab/core work, to activate the core (but your situation is quite different, since you do abs at a completely different time, which I think could work well also).
You might want to try it the way it is on the video once in a while, at least, just for a change, and to see if that change works for you.