Why did Daenerys Targaryen feel betrayed by Doreah?

Question

I did not understand this bit, I thought Doreah chose to be with Xaro Xhoan Daxos to save Daenerys life?

thus Daenerys somehow felt betrayed and sentenced her to death inside the giant vault along with Xaro Xhoan.

Answer 1

Let's see the situation from Daenerys's eyes:

1. She returns to the palace to find many of her men and a faithful handmaiden (Irri) dead.
2. Not only that, but her precious dragons, her babies, missing. Her other trusted handmaiden (Doreah) is also missing.
3. She spends many days, nervous and afraid, as she looks for the missing dragons.
4. Once she finally finds out where they are hidden she has to go through an extremely dangerous and stressful ordeal (the House of the Undying) in order to get them back.
5. When she figures out that Xaro Xohan Daxos was responsible for the kidnapping in the first place, she also finds out that Doreah is safe and sound and in his company.
6. Danny deduces that Doreah had sold her out to Xaro in order to keep herself safe and win the wealthy man's favor.
7. Doreah protests that she all did it to keep Danny safe, but at this point of time she only has Doreah's word that this is true, and Danny has no reason to believe her at that moment.

In short, the whole ordeal has made Danny a less trusting person (the lesson she thanks Xaro for), and now sees Doreah as a traitor who deserves death.

Did Doreah really do what she did to save Danny's life? Perhaps. But the price (the death of Irri and the kidnapping of the dragons) was too high to justify it in Danny's eyes.

Also, in a deleted scene it is revealed that Doreah herself killed Irri with a strangling cord when Irri walked in to find the dragons in cages, so it is truly a life for a life.

Answer 2

Well, let's see...

1. Daenerys' dragons are gone and her friend and handmaiden Irri is found dead
2. She risks her life trying to find her babies (dragons)
3. Danny finds Doreah in bed with Xaro

Well Danny sees Doreah as a common whore and not her friend at all in the end, so she locked her (and Xaro) up in that vault for good reason.

Think about it, if you were in Daenery' place.