Since Rock Fortress City and the Soulania Kingdom had decided to sign an equal rights contract then both sides had to show their goodwill with the deal.
Not to mention that if everything went great, Tianlong Yun might end up marrying the 3rd princess of the Soulania Kingdom, or one of her sisters.
Just because he was going to marry her though, it didn't mean that she was going to directly become his official wife.
Tianlong Yun had his own consideration for his Harem, and Tianlong Xia understood the same as well.
Since she had already been part of the Royal Dragon Emperor Harem once upon a time, she knew how to take care, and lead it well.
If a woman wasn't able to gain Tianlong Yun's attention, care, and trust she would never be able to reach something more than just a bed warmer.
There were a lot of women in the Shadow Clan, and his Harem who could only be his bed warmers and nothing more.