It all depends on the person. In all honestly, she has only been talking for about ten years. She didn't talk for the first ten years of her life without nonverbal help. Remember, she had her first "conversation" with her mother after she turned ten years old. She was mute (with humans) up until that point.
She does speak in a more....complete fashion depending on what she is talking about and whom she is talking to.
This is relatively new to her, discussing death without a hornet to help her out. She did just kill a lot of people in a variety of different ways and now is struggling to understand an unknown, brand new emotional reaction to killing and whether or not she should tell Shoko about it. She has a lot of her mind. She is smart and can plan, think, and analyze like an adult (the savant aspect) but like most autistic savants, she has trouble with coping with having am advanced mind but the inability to express it. Some (like Daniel Tammet) have to really work at appearing normal. (However, Daniel Tammet can actually explain how he thinks, nearly every other autistic savant cannot. Remi cannot explain how she thinks, she barely understands). So when she is overwhelmed, she retreats to her comfor zone:Basic words, basic sentences, basic understanding of emotions.
Everything she says is connected to each other, but makes little sense to those unused to the way she talk or don't pay attention.
