Crazy Cat Lady (25 player)

It also doesnt reward hard-mode loot.

Ignis the Furnace Master, Razorscale, Kologarn, and Auriaya do not have hard modes.

Source

I'm keeping this comment here as clarity for people who might believe this is her hard mode.

EDIT: To elaborate on the OP's post, it appears this achievement is really easy without doing much.
If you go for the other Auriaya achievement (In which you kill the Feral Defender 9 times to make it stay dead) you're taking enough time to kill the newly spawned add (or off tanking the add but doing low raidwide dps to the boss herself) that the Sanctum Sentries respawn during the fight and patrol their original route, thus they're alive when you kill her and get the achievement.
EDIT #2: Hotfixed: The Auriaya encounter has received the following changes: Sanctum Sentries should no longer spawn while Auriaya is in combat...
Source
Which clearly means no more getting this achievement for doing the fight normally.

You just need to nuke Auriaya while not damaging her cats. Just take off your legendary cloak and dont use aoe-spells. Should be pretty easy

Easily the hardest achievement for the meta. In every group, there's always some idiot that doesn't understand that AoE and cleaving is bad.