This one is unmissable, but i'll try to keep it spoiler-free. The enemy is tough, she'll use biotic waves to knock you out of cover, so listen for Liara calling them out. The enimy has a biotic barrier, armmor, and health. And after taking down half of the biotic barrier, she runs off and more eclipse mercs and rocket turrets. Use the cover near the back, and watch out for the rockets. After taking them out the boss will come back. Careful for when she uses a biotic move that lets her jump around the map, so she could get you from any angle. Try to keep your teammates alive for as long as possible, and dont go for close quaters attacks, snipe her out. When shes in the open, Liaras attacks work great, so take that oppertunity to get in a few golden headshots.
This may take 7-13 minutes on average, but she's basically just an upgraded Asari Vanguard.