This is set in third year now Luna first came to hogwarts in second
The two girls, somewhat embarrassed, entered the compartment. Skyler decided to make formal introductions. "Allow me to introduce you both. This is a new friend I made today, Miss Luna Lovegood. She's from Ravenclaw, a year younger than us, but she knows many fascinating things..."
Red grunted, a hint of approval in his voice. "We'll see, kid. Show me what you're made of, and we might just have ourselves an interesting partnership."
"What would these people you speak of have me do instead? What would they expect if the Martells decided that they want to get revenge for the dragon's wroth and started burning cities? Marriage is a quick and peaceful way to prevent anything like that from happening with the Martells becoming family to House Targaryen. Dorne will end up being a part of the rest of the kingdoms and there will be peace so what can they even complain about?" Likely their wounded pride that the Dornish are joining through marriage and they joined through bending the knee or burning.