Anything under 5 is a definite neg.
hcg doubles every two days approximately, and implantation occurs at app. one week before your period is due. so if she is ovulating regularly, by even a week past her period due date, the hcg should be in the thousands, not less than one.
So unfortunately, she may have had an annovulatory cycle and skipped a period.
I hope she gets her bfp soon.

Also, a progesterone blood test can show if she did indeed ovulate.