Stand by Me

Easiest way to do this achievement after multiple pulls, goes as following:

1. Pull boss, keep a slow debuff on her. (We used warrior hamstring)
2. When 2nd phase comes (She jumps on the boat) kill of the cannoneer and interrupt the boss (Using cannoneer's cannon) before she casts her ''Barrage'' this will keep the achievement progress ''white'' when tracked.
3. Kill boss (repeat step 2 on 2nd Boat phase)

Some extra info:
If it turns red, instantly wipe it.
If its red before the pull because it failed on previous pull, you can reset the boss to turn the achievement tracker white again

Don't forget to track the achievement, if it turns red instantly wipe it.
We also used 4 dps and 1 tank, as healing wasn't needed, makes it less of a hassle.

A small clip of it in action:
https://clips.twitch.tv/OilyCrunchyPonyYouWHY

When trying to do this achievement, we found that no matter if we actually rooted or hamstring'ed her during the transition or not, the achievement always failed whenever the [spell=268443] fired, so we just made sure to beat it. You have ~10 seconds before this happens in the transition, so make sure to kill the cannoneer and fire as soon as possible to bring her back. We got the achievement the first attempt after we focused on this instead of maintaining a root during the transition.

Simple when overgeared, just lust and kill.