It is true that mentors forget that a trainee is a trainee and not an experienced teacher. It's like driving behind a learner driver, they are doing it all 'correctly' but they never seem to be driving the way you want them to. Teachers are like that. What you can do of course is ask for real examples of how to achieve what she wants. Ask to observe her and both of you could analyse her lesson - perhaps she would be prepared to vide herself teaching and review that with you - teachers also often do not see their own faults even if they are the same as the faults they pick up in you.
You can also ask for a lesson that just focusses on the positives - that just looks for all the things you do 'well' rather than criticisms. That is a useful mentoring technique that works when a trainee is lacking confidence.