[X] Consider her request for a moment, as if genuinely surprised. In truth, you somewhat are.
-[X] "I'll speak to Lady Vaela myself, and if she is amenable, transport her here to speak with you." Making it clear you're reluctant to force her into returning. "If nothing else, unless she was given cause to harden her heart against entreaties to take up her duties as heir, she should at least be willing to discuss the matter with you in person."
-[X] Make eye contact with Teora, "Perhaps her sister would be willing to meet with her on your behalf? From what little I know of Lady Vaela, there isn't any rift between siblings to worry about."
-[X] Take Teora to the House of Mirrors first, and explain to her, in exhaustive details, what it is used for, first from a mercantile perspective, and then from an intelligence gathering one.
-[X] "Your reckless actions were doomed from the start, if Prince Doran can deduce the truth of your folly with far less resources than I possess. You are going to fix this."
-[X] You aren't actually entirely certain how she'll react to you calling her on her ill-fated plot, but given your prior history with trying to strong-arm impulsive people into following your lead, you are just going to assume if you actually get to this point she will have an appropriately dramatic reveal that makes a bald threat pointless, at least until she actually plays her hand.
At this point, I'm re-writing the end of my vote mostly because I am convinced that we are cursed when it comes to actually making threats during appropriately dramatic moments. She's probably going to blurt something out that vastly over-complicates what should be a simple resolution and I think it is best we move through the five stages of grief already and skip to "acceptance".