Marcella had her doubts about Paul Romano especially Mark Paulo's presence in Romano's house. The only reason she couldn't continue that thought was because Andrew died with Marcella. Even Paul wouldn't have let his son die.
After knowing that Paul is Tony's father, she stopped thinking about that. Even though Tony doesn't agree, he should have some love for his father. She didn't want to accuse his father of killing his brother to him.
But if Tony is thinking Paul did it there might be some proof of it.
She felt bad for Tony. Not only did Paul never accept Tony as his son but also, he could have been responsible for the death of the son he acknowledged. Tony loved his brother. It must hurt.
She still wanted to wait for proof. Because of the way the couple acted, she didn't think Paul expected Andrew to die.
