Leilanna paused in thought for a moment before replying. "I told you you would not be freed until you told me everything that this device, this "a'dam" can do. What are you not telling me?"

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I'd assume between Leilanna's +9 sense motive and the a'dam, she can work out that there's something the woman isn't saying (I think the a'dam gives you an indication when the person is being deceitful?).
If not, it's pretty standard practice to assume that someone in this situation is holding back information :)