Wont start if you dont leave the Whole region itself. At least by my experience.
Alissa, needs time to go there, and she will only go when you are not in Transylvania, it happens often enough that leaving 1-3 times should do the trick.
Talk to Cassie, after finding her at the Dungeon, when she Mentions Alissa, barely coming home the Quest would lead you back to Transylvania,Capture or simply call her.
Sometimes it takes a few tries till she Pops up in Transylvania, so just travel away, and travel back.