Hello Lilikar;-)
If your niece is a beginner I`d suggest these stories to start with (or as addition to a course book of your choice):
http://www.teachingenglishgames.com/eslstory.htm
Stories come with pre- and post stories games, flashcards and songs and lesson plans so don`t need to make lessons from the scratch. It saves a lot of my time.
That`s what I do with my son (9 years old) twice or three times a week.
And here you can find some suggestions and games for one to one teaching
http://www.homeenglishteacher.com/
I hope this helps,
Ewelina