Need some help shaping the world after Tiamat got summoned into this world

So Tiamat managed to sneak into the material plane of our homebrew world and I could use some help with how to move forward.

The party is at the moment no match for Tiamat and it is something that the party will have to deal with but not before they hit level 15 or something like that probably.

So how would Tiamat react and what things would be logical to happen?
Would Tiamat just cause havoc in all kind of cities or is it more likely Tiamat will find a good place to create her lair?
I would assume a lot of evil creatures would follow her or maybe want to get rid of her and could become some sort of alliance with the party?

Anyone had Tiamat in their campaign and how did it work out?