addon to keep slave facing target?

[Ualaa]

You can use Interact With Target, if you have Click to Move enabled.
Press your IWT keybind, and then follow with backwards movement to break the movement.
The range on IWT is approximately 3x further then follow.

You can also use Jade Channeling Crystals, which cause a beam of light to move from your toon to the target, and incidentally causes you to face the target.

There isn't anything to prevent your toon from turning.
Nor is there anything to automatically have your toon turn as the target moves.

[Akoko]

Nor is there anything to automatically have your toon turn as the target moves.

Except Arcane Missiles or other targeted channeled spell.

Still, what the OP asks for sounds like botting to me.