I need help wih a pregnancy test? help please?

My girl took a pregnancy test around 2 30 pm. It came out negative. I came on her on 11-10-2010, her period is due between 20 to 23, she says she been having a stomach pain when her period is close.. Can she really not be pregnant after i came on her which it was a lot? I know it has to be in the morning for it to be accurate. But she just wanted to see what it said. Do they always come out negative when is not on the right time??