Is 6 False Positives possible?

My sister took 4 first response tests all with dark positive lines. I told her to take the digital test and took too clear blue digital tests and it said "pregnant ". She went to the Doctor and had a urine test and blood test done, and it came back negative. Is that possible to get 6 positive tests and still get negative tests at the doctor? I can see a couple of false Positives, but 6?!?!? Has anyone has this many false Positives on these tests and should she seek another opinion? I told her she should, but she said thinks her period is coming.