Wa alaykum salam,
There is no need for her to 'deal' with her father. She shouldn't have the mentality that she needs to challenge him.
She needs be patient and ignore any actions that are contrary to Islam. Holding ones tongue and remaining patient is often the best response when people say or do crazy things, especially when there is ego involved (that of the father). Face it, it takes a lot for parents to drop their ego when their behaviour is being objected by their own children. It's not going to happen. She needs to
realise her place and act accordingly. You can't go into a king's palace and order the king about. Maybe if you went in with some gifts though, he will listen willingly.
The result that she yearns to happen is for him to become a better muslim. If he's not willing to listen directly, then she needs to be indirect about it. Use tact and wisdom to gradually change his view. No need to be aggressive about it.
Has she heard the anecdote of how the Grandsons of the Prophet Muhammad Sallalahu Alaihe Wassalam, Hassan RA and Hussain RA, in their wisdom, rectified the mistake of an old man who was performing ablution in contradiction to the sunnah?
"An old man sat to do his wudhu. But his wudhu was not correct. Hasan and Hussain the grandsons of the Prophet (S.A.W.), then two young boys, watched him. They immediately realized that the old man was not doing his wudhu correctly, but hesitated to tell him directly. Perhaps the old man would feel humiliated by two young boys, or he might even lose interest in the act of worship.
Sitting next to him, they started to do the wudhu and during the wudhu, Hasan said: "Oh Hussain my wudhu is correct and more perfect than yours."
In reply, Hussain insisted that his own wudhu was better than Hasan's.
Finally they said: "Let us refer to this gentleman. He is older than us and should be able to decide."
The old man was listening patiently. The boys performed their wudhu under his supervision, one after the other. And when they had finished, he realized the wudhu done by the boys was methodical and correct. It was his own wudhu which was incorrect. Turning to Hasan and Hussain, he gently said: "The wudhu done by you is correct. I am grateful that you chose to guide me in such a beautiful manner."