Student teaching is hard, especially if the teaching styles of the coop
teacher and student teacher don't mesh. I'm guessing that the s.t. is
afraid that she can't teach like you, and she knows her grade and whole
career (unfortunately) rides on whether or not you like what she does. The
stress must be getting to her, and she is procrastinating. Perhaps you
could reinforce the fact that you are there to help, and that she needs to
go ahead and try her own ideas. Remind her that teaching is stressful,
especially at first, and she's going to have to get used to working with
many people, kids, parents, colleagues, administrators. She has to dive in
with confidence if she wants to succeed.
One final note, I found my first experience as cooperating teacher hard.
It's difficult to watch someone else take over your classroom. I've had two
student teachers now, and I'm becoming more comfortable in my role, and I
find it a bit easier to let go. Good luck.