I'm DMing a Tyranny of Dragons Campaign. One character made a deal with Mammon after a dragon wantonly killed her family in their home. She accepted the fiend's offer out of hope that she would one day get revenge. Mammon, knowing that worshippers of Tiamat were slowly starting to prepare for her resurrection, wanted this character to learn as much as she could about the dragon worshippers, their plans, and where Tiamat would be resurrected.

That's the hook for the warlock of my story. I am looking for suggestions as to what dragon i can have been the killer of the family. If possible, id like it to be a dragon that would make sense for a level maybe 7 or 8 party to fight, but also to be as lore-faithful as possible.

I dont know too much about lesser dragons. Worst case, i create one of my own, but if there are any specific dragons that follow Tiamat and would fit, i would love to hear about it!

Edit: I was hoping more for an existing dragon that would exist in the world. Creating an original one isn't an issue, but identifying one that would fit in the world and in the story is another thing.