Some had said that could be cause there is a change in her character. You know, wearing trousers as boys could be meaning that she is strong like boys or some thing. And look at this:
From
The Daily Record Quote:
| Harry also finds his head turned by pal Ron Weasley's sister Ginny and Cho, played by Katie Leung, 19, from Motherwell, Lanarkshire. |
So, i don't know if they will make Harry and Ginny share moments or not.