it could be that she took it too early or it could be b/c she is stressing over it that's why she is late. but it really sounds more like she is pregnant and she took a test too early so take one again to make sure.
she took the pregnancy test too early....she needs to take one now.
If she is six days late and the last time she took a pg test was 6 days before her missed period, then she should be able to take one now and get accurate results!