Arianna didn't come out of her room all day, however, she ate and Marcel was grateful for that. It was something at least because if she planned on starving herself then he would have no choice but to force the food down her throat. But for the fear of choking - he heard people died from that - he would have to threaten one of her family members and she would only hate him further.
Marcel was trying to be gentle with her but Arianna was not making it easy either. If she was only damn obedient, then this would have been much easier. However, trust Arianna, she would butt heads with him in every decision and action. She doesn't trust him one bit. Well, he hadn't given her a reason to do so. Even at that, the Arianna he knew would never do as he said even if he asked her.
So no, trust was impossible.
Thankfully, Marcel was busy with meetings all day. He had to strengthen his influence in the city including his control over local enforcement partners.