Naming Family Members

This video was actually recorded about half a year ago but I was not sure if I should share with family and friends. Why? When my sis watched it, her first comment was "Why are you so fierce with her? How come you didnt praise her at all? Children must be praised." My defence is "I was too engrossed with the recording that I had forgotten all about praising."
Of course, I do praise her (very often) and I try to make learning fun most of the time. However, when her attention begins to wander, that's when my tone turns authoritarian. Is this an educationist's habit? Do most if not all teachers have the same tone?
Despite all these, I think she is doing quite well in learning the language. Her only problem is that she needs more exposure to English speaking environment. Although we speak to her in English, she doesnt hear us communicate in that language. All of us converse in Cantonese. This has caused her to catch up Chinese/Mandarin faster than English nowadays. Her ability to speak BM is at about 30words.