She might be in that spot in her teaching career where she can change things at the last minute and still achieve something. My mentor told me at the end of my experience that he never wants to let his student teacher down, so he always made sure I knew what would happen the night before class. Each night, we would discuss the next day, and I would watch him teach our morning class, and then I would teach our later classes. I think it is unfair for your mentor to change things all the time. She might be able to do it and not encounter any issues, but she has to remember that new teachers are not typically able to wing things. I am not sure how many student teachers she has had before you, but mine had six before me, so he knew how to handle a student teacher. My mentor would be so specific and explicit that he would send me lesson plans with projected times for each activity, which I really appreciated. I student-taught seventh-grade ELA, and that was a unique experience because the curriculum was very focused on the state testing. My mentor was so worried about his state test scores, so we did a lot of co-teaching. I had my moments to shine, but I followed a lot of what he did because he wanted things to go a certain way. I still had moments where I could be creative, however. We had a general pacing guide and then specific lessons in each unit.