Can a hair strand test be a false positive?

Possible but highly unlikely.

Can tests be screwed up? Yes. Can people lie? Yes. Can drug users forget? Yes. Can drugs be ingested without intent? Yes.

the tip of a 12 inch piece of hair is from 48 to 96 months ago . was she doing back then ?

Hair strand analysis is extremely accurate and very few false positives come from it however you have to realize that you never ever give your hair strand analysis to your legal adversary. They may tamper with or simply report to the judge that your sample was positive for a drug in order to continue with their case! If the person is truly free from drugs the person should approach the judge and say I believe the test is in error and I would like to pay for an independent laboratory to redo the test. If the test comes back negative the person that is retesting needs to immediately submit it to the judge and say judge I want to have this test confirmed buy another independent laboratory. That way you will have two negative tests to overrule the positive test and the judge will dismiss the other positive test

Possible but unlikely. They usually retest any positives for confirmation.

Hair tests can lead to false positive results because certain drugs — like cocaine — which are found on common surfaces, including dollar bills, can be absorbed into hair. There is currently no way to fully cleanse hair of these drugs.

But PROVING it is very hard.