How do l control my "anger" when my assessor comes tomorrow?

l am doing an apprenticeship and so far l am doing extremely well! But the problem is my assessor. She's such a ***** and she pushes me to do things ALL THE TIME! l get things done in my own time and my way, but when she's there she constantly tells me what to do first, then she tells me to hurry up when l am trying to sign forms, and when l photocopy things she moans at me saying l shouldn't be doing too much as it 'wastes' time, but it's my job and that's what l am being asked to do! Last time l shouted at her in frustration because of it but l have one more warning left, how can l just tell her to back the hell off? :/