You have to be level 190+ to enter this area through its front "door".
Entrance is located right alongside Dustbrigade outpost and the method of entering is quite similar as well. All you have to do is to right-click on Dust Brigade Security Codes and then step in center of blue circles. Ok, one more thing is needed, namely that you're in team.
Once inside, you'll be facing a corridor that leads to main and only room. But before you face Ground Chief Aune, it would be a good idea to get rid of 8 Masked Commandos that are lining the circular outer walls of main room. While you can kill them, they have a nasty habit of respawning. Easier and safer is that either tank or doctor trains them to start of corridor and that somebody in team calms them there. That way anyone dying has a far chance of zoning back behind their aggro range, or should he/she aggro them, it will be just a couple of them.
Now you should be ready to face Ground Chief Aune, located in the center of Machine. Unfortunately only way to get to her is to walk narrow pathways traversing a fan of sorts. Good idea at this point is to turn off run mode, since there's realistic chance of falling off the pathways. If you find your self in the unlucky stituation of falling off you can do following. Run counter clockwise, you will notice that the four platforms will light up with colors this will teleport you back up.
Like most encounters, Aune has couple of tricks beside decent damage. First of it you'll encounter soon enough, since she'll warp to different pathway, stunning everyone in range in the process. This one isn't that bad, since if you enable run again, you can jump from one pathway to the other. Just be careful not to do so in middle of earthquake, since you can loose your footing. Her other tricks can be harder to deal with, but if team follows vicinity chat, they can detect it in time, since she shouts related phrases:
Ground Chief Aune shouts: Shoot me cowards!
Ground Chief Aune shouts: Go ahead! Shoot me!
This will force Blessing of the Enemy (red nano effect)in your NCU. That way, you'll heal Aune for over 14k with each hit (DoTs, perks and pet damage excluded). Best way to battle this is to assign one team member (he/she will probably have to have some healing ability) to staying close to outer wall. Once she/he hears this phrase, he should circle the outer wall, searching for towers to kill. Once disposed of tower, it's safe to attack again.
Ground Chief Aune shouts: You will never know the secrets of the Machine!
This will be associated with blue nano effect and will provide Aune with absorbs as well as 200 point reflect shield. Tactics should be the same as above.
Ground Chief Aune shouts: Know the power of Xan!
shortly followed by
Ground Chief Aune shouts: Die!
First shout initiates a Machine Shockwave and the second one Notum Pull. At the same time Notum Irregularity will spawn somewhere on pathways. Beside emmiting light white nano effect, you can target it as Omni and even see it on minimap. Stepping inside this nano cloud will clear init debuff as well as prevent being hit by DoT. However, Notum Irregularity has short duration, so you better get there as soon as possible. So the team member that's on tower watch will probably missed it (that's why I suggest to get somebody with heals on task).
That's basically all the info you need to be able to kill Aune. In case of a wipe, the tower watch member will probably survive, while maintaining aggro and preventing Aune to heal. In such case, team should discuss about returning to same instance, since they'll suffer a bit less of her tricks as well as fighting already damaged mob. But this is only possible if those Masked Commandos were pulled and been calmed in proper location.
Ground Chief Aune has more or less standard inventory: