Ziva didn't know if it was a good idea to make such a decision. But she also didn't need her father snooping around her life once she stepped on to the nice summers Israeli ground. As much as she missed the weather of her hometown she knew she had to move on. Her father has already ordered her back and she is disobeying the order. She couldn't keep saying no for much longer or else SECNAV will order her to go back and never come back unless her father lets her come back. They can't just cause problems and wars between countries just for Ziva and she knows that. So she thinks that she made the right call in becoming an agent.
She doesn't know exactly how he will react. But she knows that he won't take it well so announcing to him that she will no longer work for Mossad and no longer be Israeli won't be easy. They have a very delicate situation in hand and it needs to be dealt with kid gloves. He also needs to be called out for trying to kill her, her partner and her boss in more ways than once. Two counts of attempted murder and one for kidnapping. That might be about 35 years in prison. Not to mention trying to kill DiNozzo twice and Gibbs once. It ends with life in jail and thankfully not GITMO. Ziva didn't want to sent him to jail forever but she didn't want him to be on the loose and to be able to hire anyone to kill anyone. She loved her father. She really did. After all he is all she has left. She can't emphasise how much she still loves her father even after all he has done. She still loves him. She also loves her team. Abby, Gibbs, McGee, Ducky, Jimmy, Jenny... Tony. She loves them all. Some more than others... But she still loves them all. She doesn't want them getting hurt either. Some have already been. More than once and that can't keep going because of him. Some how the Americans were going to have to try and convince the Israeli government to give up the director of their intelligence agency. They have a lot of things to discuss but not a lot of time. Sooner or later, the Americans will be forced to turn Ziva up. If she doesn't become American soon enough she will be in a way, deported and the country will forbid her from coming back. Things had to happen FAST.