On Heroic, Hagara runs while doing Focused Assault, so you cannot simply move out of distance like on normal. You can ping pong her by having a ranged player taunt and the tank taunt back. If your tank is a warrior, you could probably Heroic Leap or Intervene to kite.
Taunt has
diminishing returns after the fifth taunt. This isn't an issue when Hagara only does two Focused Assaults (requiring four taunts total if you're using the ping ponging tactic), but does come into play if a phase has enough time for her to do three Focused Assaults. Our group handles this by the tank using heavy mitigation cooldowns when players are tombed to manually survive the assault.