First day of third grade

2 pm:  Today is the first day of the experiment that is homeschooling third grade.  The first half of the day went well.  We started easy and stayed on task.  There was a break after 3rd period and we have taken a long time getting back into 4th period.  4th is Science.  Each day in Science Kiera must define her new terms, read the passage, and answer the questions about what she read.  This should be easy, but we are having a disagreement about how much she should have to write down.  I have tried to explain to her that third grade marks a new way of schooling.  That there is more serious work even in the public school system.  She doesn't believe me though, and that is part of the problem.  After arguing for nearly an hour with her and trying to explain all this, and when I got to the point that I wanted to cry and rip her book in half at the same time, she finally agreed to write down her definitions.  This however, has taken about 45 minutes for her to write down four words and their meaning.  She is so easily distracted and it is very frustrating.  I don't want to spend all day yelling at her to stay on task, but I'm not sure how to keep her on task.

4 pm:  I am going to lose my mind!  What was I thinking?  She doesn't take me seriously as a teacher.  I don't want to have to yell at her, but keeping her on task is going to give me even more gray hair than I am already getting.  But I won't give up.  Not on the first day.  I think that it will probably take at least two weeks to fall into a routine with the classroom.  
I do worry that I'm going to fail to actually teach her.  How did any of us actually learn in the classroom?  I personally don't remember much of anything that I learned in school.  Oh sure the basics are there but I couldn't tell you what a participle is.  I can't list the U.S. Presidents in order.  I can't tell you all the state capitals.  So how do we learn? And what do we need to learn?  And how bad am I going to screw this up?