Put this together with the savior achievement.
Adopt all little sisters, each little sister gets you 2 gathers.
During this achievement you can also earn 'Master Protector'.
For Master Protector, there is one that will definitely earn you the achievement.
In Siren Alley, you come to a Big Daddy and Little Sister in the first room you visit. Kill him, adopt the baby girl and go upstairs to the balconies in this room.
There is an angel in the edge of the stairs on the balconies.
Put traps on the bridge and at the bottom of the stairs. Others around the corner on the balcony.
If you have proximity mines, use those as well.
Put the Little sister down and hide in a room behind her. Your traps should do all of the work. But a few may get through. None will get the surprise on you. So don't worry too much.
To couple it with savior, you need to save three other people too.
Grace, Gil and Stanley. When given the option to kill them, just turn your back on them and walk away to comtinue the story path.