The locked door is one way to get to her. Have you found the cave system yet? Look for a room (Maybe level 3?) With a huge mother of a hole in the wall. Go thru it into the cave system. Remember there are TWO cave system, one has three doors to seperate levels of the vault, with mantis' everywhere.
You want the cave system that has no doors, and just has the hole, follow it down into a MASSIVE cavern filled with the venus flytrap looking things. You'll find her sitting in a little alcove near the back of the room. Just keep searching.
Also, there is a part up ahead, where EVERYONE seems to get stuck on. I'm putting the solution in spoilers, you will know when you get there.
Don't open if you want to do it on your own!
Spoiler *COPIED AND PASTED FROM OTHER THREAD
Ok, heres what I did.
First, go back to Ghoul lady.
There is a duffle bag in one of the room corners, get some grenades.
You'd think you could sruvive in any room, but from what I can tell you HAVE to be in the room where you downlaoded the terminal information. Its right to the left of the vents. Throw grenade, immediatly press door button, and you should survive. The other rooms wont work, as even with doors closed you will still die.