the treasure that you find inside the Sierra Madre Vault when you finish the DLC would be precisely Vera Keyes ghoulified alive. After all, Frederick Sinclair said the vault was designed to protect the Sierra Madre most valuable treasure: Vera Keyes.

Perhaps at the moment the holograms started to lassering all the guests, Vera Keyes could have seeked refuge in the Vault...once she got there she wasn't able to get out, and the radiation/the cloud could have ghoulified and preserved her, just as it happened to Dean Domino.  But I guess she would have lost her marbles after being locked up alone in that reduced space for so many years...

Another possibility could be she wandered around the Villa for years like Dean Domino did.

A last one would be she and Sinclair bump into each other there and survived together inside the vault as ghouls.

She supposedly was very ill and was going to die anyway, but I considered the chance she could have been healed by radiation, just as those guys in Lone Some Road DLC.

instead of Vera losing her marbles the vault room was suppose to be a different design sort of like a advanced auto doc that kept her in stasis and asleep, but radiation leaked in and ghoulified her resulting in the model. The outcome of the Sera Madre was probably suppose to be a lot different, but I suppose Bethesda agrees with me here, a rescue a princess in a tower situation wouldn't have made for a very interesting story and instead did what they did now with such a sad one instead.  

I have seen a lot of sad groups in my time, made up of players from different games trying to get in on the Jackpot.
Think of us all as a deck of playing cards. Now, we start with the numbers. You got two kinds, The Holograms and The Ghost People. All they are, are numbers. That doesnt mean their not a threat, but it does mean theres bigger fish out there.
Then theres the big cards. The King, Queen, Jack and Ace.
The Old Mans the king. The man in charge, and the one who thinks he can do anything and everything.
The Queen, is our little mute. She clearly has a large part to play in this, otherwise why keep her alive. She clearly hates the old man, but then again we all do.
(Courier asks does that make Dean the ace)
No. I am the Jack.
(Courier asks why)
In old fairy tales, the Jack was almost always a thief. Needing something from another and taking it for his own. As a former Jack of this trade, I think its rather fitting.
(Courier then asks if he's the ace.)
No the big one is.
You are the Joker. The one thats not supposed to be in the deck. In other words, You are the wildcard.

I thought it would have been nice if the gold was fake(still heavy because the moral is to not be greedy like Dead or Elijah). But its revealed if we go deeper into the larger Vault that the true treasure was in fact the positive pregnancy test belonging to Vera. That the true treasure was that her and Sinclair were to have a child, which explained her depression (she was unaware of the fact she was pregnant). And the vault was to be a safe haven for the new family should the bombs ever drop. Nothing of true value in the vault bare things of sentimental value to Vera and Sinclair, and a holotape expressing Sinclair's desire to make Vera, an honest woman. Irony being that she was conning him the whole time.
A little sappy,yes. But in the end, the man made an entire casino for her. Who knows how obsessive and in love he was.