RoughCoronet0
Dragon Lover
I'd imagine this isn't a creature you are meant to fight in a conventional campaign. She is a god after all.I'm not entirely clear how characters are supposed to fight this thing when it deals enough damage to level a raging 20th level Barbarian in a single round.
If I was to use this Tiamat a good chunk of the campaign, especially the higher level sections, world be centered around collecting powerful boons, divine allies, and artifacts that could help the party's chances of fighting her on a more level playing field.