The bitch is back and this Achievement can be very tough. I attempted it for almost 3 hours with no luck on Easy and I had 4 Explosive Bolts, 2 Lightning Bolts, 4 Grenades and ALOT of Ammunition. I burnt every body and hit every valve and nothing killed her so like most I loaded it up on New Game and I would advise anyone going for it to save your sanity and do the same.
With the Rocket Launcher it doesn't take much to kill Laura. So still do the same things,
Light Bodies
Light Valves
Use the Explosives on her