What does my boss think of me?

My manager treats me badly during month end close. I know she is under pressure during this time but for small small things she will come back very badly. If i try to sort things she not respond properly like a type of cold war. Once its over she will be normal with me. She will ask me to attend client calls ok behalf of her, ask me to support and guide another colleague. There are times when she says if all the activities are completed pls dont stretch..log out. Im unable to understand her. Please let me know what is the sort of impression she has on me so that i can handle accordingly.