She is a white painted bride and it is a Bulgarian Muslim tradition that very few people practice. Under Communism, many religious traditions were banned and few communities revisited those traditions after Communist rule was lifted:
Bulgaria is the only European Union nation where Muslims’ share is as high as 12 percent. The communist regime, which did not tolerate any religious rituals, tried to forcibly integrate Muslims into Bulgaria’s largely Christian Orthodox population, pressing them to abandon wearing their traditional outfits and adopt Slavonic names.
The wedding ritual was resurrected with vigor among the Pomaks — Slavs who converted to Islam under Ottoman rule and now make up 2.5 percent of Bulgaria’s 7.8 million population — after communism collapsed in 1989.
But today it is still performed only in the closed society of Ribnovo and one other village in the Balkan country. Young men return from abroad to the crisp mountain snows, just for the winter weddings.
People in Ribnovo identify themselves more by their religion, as Muslims, than by their ethnicity or nationality, and the wedding ceremony is an expression of their piety. The village has 10 clerics and two mosques for 3,500 inhabitants. (Source)
Here is another photo.