No.
it will almost certainly be positive, did you feel the effects of the xanax? even if you didnt, taking a test the next day will most likely show a positive result
The way to pass any drug test is not to take that drug. If you've already taken it, it's a bit late to be worrying about passing the test.
if your asking if you take half a xanax, and have a drug test the same day, will you pass? Then my friend the answer is no. Xanax half life is 6-12 hours. If you took it extremely early in the morning, and it was half of a 0.25 mg pill, you might have a 2% chance of passing.
If you test dirty yes they can. Or if you have another outstanding warrant for your arrest.
Will you pass a swab drug test if you passed a urine drug test on the same day?
youll be dirty for THC and opiates
I failed a drug test for my doctor. then later that day wrecked my car. They didn't screen me. But can they go back and use the previous drug screen from earlier that day to prosecute me for a DUI?
Yes, but lab will confirm the drug properties as no harmful.
The next day as in the day after she does drugs? If she is fully aware she has a test the next day and does not have the control to keep from doing drugs, then maybe the concern should be more for your cousins well being than helping her beat a drug test. See the related link below.
nope...not taking any drugs helps pass a drug test.
Pray