somehting for sharing: no need explain to her, you can simply tell her when is the time she can turn on the TV for your kid. In my side, my son off school back home at 4;45, she will help my son take a bath first, and then eat snack, and then doing homework and sit with him, drawing, story time. i tell her she only can turn on TV at 6:00. my helper spend 3 months and she can do this routine. i think you better tell her your house rule, and tell her play and stay with your son is her job rather than stay in the kitchen or just turn on the TV.
Sorry its hard for me to type chinese