Mother of Dragons is just a title given to her after live baby dragons were born from stone eggs that she owned (during a ritual of sorts). Like other Targs, she bonded to her dragons. Nothing in the story suggests she can control all dragons, and with undead-Viserion being ridden and controlled by the NK, I doubt…

:-D Yes! Does anything else in rl make blue fire?

How do all the Winterfell ravens, for example, know how to get to all the different keeps and towns around Westeros, if they only know how to get home?

Viserion was “magical” in life, the other wights were not.