A eunuch caught these two behaving affectionately toward each other as teenagers. He reported his shocking discovery to the Emperor, who was having a semi-casual conversation with Torch at the time. As casual as a conversation with the Emperor can be, that is.
Torch accused the eunuch of slander, claiming that Princess Jian is filial and would never engage in romance behind the Emperor's back. He also said that Dragon Lord Ember would not initiate such improper conduct and demanded evidence. When the eunuch failed to produce said evidence, the Emperor had him punished and thanked Torch for stopping rumors from spreading in his Imperial Court.
Torch questioned Ember about the ordeal not much later, who confirmed the eunuch's story, much to the horror of her father. The Emperor got the truth out of Jian too and was enraged. The Emperor dismissed Jian and summoned both Torch and Ember. Ember had never seen her father grovel before, but he was apparently good at it. In a foreign language, no less.
The Emperor ordered Torch and Ember to stay confined to their guest palace for the remainder of the official visit while he mulled over what to do. It was true that the behavior of Ember and Jian was essentially an act of mutiny. After all, Jian's love life was the Emperor's to determine. But after the Emperor calmed himself he realized that this romance wasn't necessarily bad news.
Jian is the Emperor's 212th daughter and he had just about run out of nobles to marry them all off to. He decided that if Ember hatched at an auspicious time and her fate didn't clash with Jian's, he'd allow the two to marry. Ember may be a dragoness, but she holds the most powerful position among dragons in the West nonetheless.
Dragon Law forbids dragons from getting married before adulthood, so Jian and her maids were locked in a palace to preserve the princess for the Dragon Lord until she was ready. Jian was okay with this. She missed her daily walks, but other than that not much had changed for her. Her movement was already incredibly restricted. At least she knew who she was marrying and she wasn't going to end up being used as an incubator by some self-important jerk.
Despite the limited amount of time Ember and Jian had spent together as teenagers, they turned out to be a great match. Completing both of their nations' royal wedding traditions took quite some time and effort, and both families received quite the dowry due to the both of them being female.
The move to the Dragon Lands is a bit rough on Jian at times. She likes that the rules of conduct are much less strict. Though there are customs she refuses to give up, such as putting her hair up in public.