Ah yes, the "make me" horse. That is a heck of an eye opening moment the day you switch from a reliable school horse to a greenie. That's the day you start becoming a trainer in addition to a rider. This is a mental thing. You know you can ride, but she knows you're nervous, (the horse) so she's pushing your buttons to see what she can get away with. Next time your on her, put all the bad stuff out of your head and just pick one goal at a time. Something as simple as walk across the diagonal, or trot 8 steps, and get it done. Pick battles you know you can win. If you get overwhelmed, the horse will too, and then it'll all be out the door. Tell yourself you can do this. If your trainer offers not so useful advice such as "what are you doing?" ask her what you should be doing to correct it. That's her job as your instructor.