Short answer: You are answering why?
Why doesn't she want to go out? She doesn't want to go out because she's in a very bad mood. She knows that she won't be good company.
Remark
The sentence after the ; (semicolon) does not begin with any kind of connective word. If you put a noun in place of she, you would see that the last part after the semicolon is a complete sentence.
