Official tosses the ball to the free thrower and all players are set for the free-throw.

Free thrower, in preparation for the free throw shot, repeatedly hits the floor over the free throw line with her shoe similar to a pitcher digging dirt in front of the pitcher rubber with his/her cleats.

Free Thrower sets and then shoots the free throw.

Is this a free throw violation?

i would never call it!!

By rule- Yes this is a violation.

I would do some preventive officiating and let free thower know that all officials may not be as nice, and may call you for a violation!

AK ref SE

This is exactly what I would do. I'd even say that I'll start calling it if it continues. To not take some sort of action is only inviting trouble from the other team if they see you ignoring it and and call them for something that seems (to them) to be equally trivial.