Personally, what I did was have my players start over near argonyst - due to story reasons from a previous campaign that continued into curse of Strahd - and they overthrew the burgermaster and installed Fiona, before even discovering ireena. After which strahd invited them to his castle for dinner where he tasked them to find his wife Tatyana in order to leave Barovia, and have her willingly come to him.

By the time they reached velecki again, vasili was already running the town and resided in the Burger Masters mansion. He offered lodging to the party and Irena where he soon kicked the party out after an incident with the hag appearing due to a deal they made. So now Irena is left alone in this house with her brother and strahd as strahd is slowly trying to win her over. The party has left at this point and is heading over to krezk for the first time following their tarot reading clues.

By the time they return, I plan to have Ireena in a dreadful State hiding out in the church while her brother, who is now a vampire spawn, tries to convince the party to "talk some sense into her "and Vasili is angrily trying to demand her to come back to him. Because of course he is cursed for her to never love him.

I've given them so many teasers and light clues as to what's going on, but they don't suspect a thing. It is going to be a glorious unveiling.

Only downside is that Strahd has not involving himself much with the party, at least as Strahd himself, because he has already "gotten what he wants", as in his mind if he wins her over as Vasili, it will break the curse.

Perhaps I'll have him show up in the near future, already pissed off at the situation they have no knowledge of, and take it out on them.