My daughter’s language

At home, our conversation is in Japanese most of the time. My daughter sounded OK with her Japanese. However, sometimes she didn't answer me when I talk to her in Japanese. Then I tried to talk to her in English. she made a kind of quick responce. This is very natural thing for her. She is in the English world everyday. These days, when I have to explain things, I have to use English to make her understand well. She can speak Japanese of course, but she can't get the delicate nuance of Japanese.