You have to understand the Sicilian culture before you could understand this marriage, and her family's consent. The Mafia began in Sicily as a form of "street justice". The Sicilians were treated like another country by the mainland, and the police were so corrupt that they were were not trusted at all by the people. The Mafia was a form of vigilante justice that was meted out in the place of a corrupt criminal justice system.

The Mafia chiefs were, therefore, revered. Remember the beginning of The Godfather, when people like Nazorine and Bonasera went to Vito for help, for justice. It was the same in Sicily, except even more so.

For Vitelli's daughter to make such a match was a stroke of luck in their culture, not something to be feared or concerned about.

Of course, the Mafia was just as corrupt as the justice system, especially as it grew more powerful.