What are the main point of arguments in Narrative Empathy by Suzanne Keane?

I assume you are referring to Suzanne Keen's pivotal 2006 article, "A Theory of Narrative Empathy"—or possibly, to Keen's further writings on the subject. In any event, all of Keen's writings about narrative empathy are key to an understanding of the concept, and all of them cover the same major points: namely, Keen explains what narrative empathy is from her perspective and then makes various arguments about how humans are affected by it.
Below I will set out, in a bullet-point format, what I believe to be Keen's major arguments. Hopefully, this will give you a skeleton to work from.
The concept of narrative empathy is the tendency of humans to identify with, share the feelings of, and otherwise see things from the point of view of people in the narratives we read, watch, or listen to. A "narrative" in this context might be a work of fiction—in which case, the writer will have written with the goal of evoking narrative empathy in the reader or viewer—but it might equally be a work of "fact," where a news story, for example, is framed in such a way that we feel sorry for or angry with the participants. Keen notes that narrative empathy is not the same as identifying with a character: it is simply the first step of sharing a character's feelings or understanding his or her position.

Narrative empathy isn't the same as either sympathy or "empathetic aversion." Readers don't normally want to feel pity for a character that lasts after reading, and they certainly don't want to really share in the distress of a character, as this can be very upsetting and cause people to stop reading. It is key to narrative empathy that the reader feels immersed in the world of the text, such that they can understand the feelings of the people in that world, but also that the world feels distinct from their own. This enables "transportation," a state in which the reader can feel fictional emotions in a real way, which can be cathartic.

Both writers and readers can experience narrative empathy, and the two don't necessarily balance each other out. Readers will not necessarily empathize with a text in the same way as the author did while writing it.

Narrative empathy can be encouraged where people do identify with characters—that is, if they feel that there are similarities between themselves and the characters concerned. Readers may also, however, simply be more inclined to experience narrative empathy if they are more empathetic people in general, in which case identification may not be necessary.

There are certain techniques which studies have found increase narrative empathy. These include: texts which "channel" the perspective of a person, certain points of view, vivid settings, and "continued storyworlds." So, for example, if we read several books about the same set of characters existing in the same universe, our narrative empathy will become increased. This is partly why people enjoy reading or watching series—they don't have to develop narrative empathy all over again, because they are already used to the characters and setting.

You may also want to read Keen's Empathy and the Novel, in which she sets out her ideas about narrative empathy in much greater detail.