How late were you when you took the test and your test was straight up possitive?
I was 6 days late and my test were still very faint after 8 days I took a clearblue digital.
@gloriaa, it takes some people longer to start producing a higher amount of HCG and if she ovulated late or implanted late that could play a role too. Just tell her to keep testing every other day or so until she either starts her period or gets a positive. If she can, it maybe more efficient to go get a blood test, those will tell you really early on.