Description is somewhat misleading. Get 50 kills with turrets, including turrets summoned by hacked cameras, is more accurate. The kill count includes flying sentrys gifted to you and the mini-turrets you can drop with the hack tool.
Obviously, hack everything. Try to always have two hacked sentries with you. The Repairman tonic will let you heal them and increase their damage, so equip that when Eleanor gives it to you. If you use the mini-turrets frequently, you'll have no trouble getting this by the end of the game.
If you should reach the end of the game without this achievement, it can be farmed. Find a hackable object; safes are best, but anything indestructible will work. Stop the needle in the red to trigger an alarm. Shock and quickly hack two sentries, going for a blue damage bonus. Let those two handle the next sentries. Repeat, replacing the sentries as needed. This'll take a while, but it'll work.
You can unlock this in the protector trials very easily. Choose a level that starts you with either hack tool mini-turrets or the Security summoning power. Sit at your little sister and let them get the kills.