It is obviously not easy to accept another man taking the place of your father. And it is also true that, more often than not, the usual negative depiction of a step relation comes close to reality. You mention that she has developed a disliking for her stepfather because of some valid reasons and that her relationship with her mother is also not very harmonious. In this situation, it is understandable that she is going through an emotional turmoil. She must be feeling very lonely in the world, the loss of her father aggravated by another man trying to take his place.
However, in my view, rather than taking up a collision course with her father, which essentially means pitting herself against her mother as well, she should try to accept the situation as it is; and develop a better relationship with her stepfather. It is very much possible that she has not understood him well or has not allowed him to develop a fatherly place in her heart. If she gives him a chance, he may start treating her well and she will also begin to like him or understand him better. A lot of our relationship problems are a direct consequence of poor communication. Developing better communication with him, forgiving him even if he is at times not very affable and making her mother realize that she is doing her best to build bridges are some of the means she can use to win him over.
Hating someone without any cause is definitely not the trait of a good Muslim. Hating for a good reason at times might not be objected to as is usually beyond one’s control; but rather than hating the patient we should hate the disease. The example of the Prophet (sws) in this regard is for all of us to emulate. He endured all gestures of hatred directed at him with utmost patience and tolerance and returned them with his most beautiful and characteristic mannerism that turned his foes into loving friends. The spirit of Islam will bring out the same character and attitude in a Muslim. God will most certainly help her in this test. She should rest assured that great reward awaits her if she only be steadfast.