If anyone has problems with it and I had, played it probably 3 or 4 times in total and it never unlocked (on PS3):
The main trick is to NOT PICK UP ANY ITEMS.
Yeah, it says use knife-only and healing is somehow fine, but it seems when you pick up anything except for keys, the trophy won't unlock.
Another trick is to switch to Moira as soon as you can and then keep controlling her. Put all weapons away, so the AI can only use knife and it should all work out.
For the part right after you put in the gear and you get attacked by quite a lot of enemies, simply keep on playing as Moira, don't attack anything. Try to get the door open. After removing one bar run to the opposite side of the hallway and wait until the enemies walked over there. Then run back and remove the 2nd bar.
Was easy as pie and after stopping to pick up anything at all the damn trophy finally unlocked.
Capcom is really silly counting AI crowbar attacks against it while not putting any option in to disable AI attacks. It's just silly. And then requiring the player to not pick up any items and not mention that at all and it doesn't even make sense, as I said healing is fine and that way you USE a herb. But picking up one is a no-go.
Any competent company would have allowed crowbar attacks as well or well just give Moira a knife.
Stealth attacks are definitely fine as well as knifing someone on the ground. Follow-Up attacks seem to not be fine, which again makes no sense because you can't control AI and knife attack button is the same as follow-up attack button.
Really badly design.