I don't know what kind of test it was. My guess is it was an "I-Cup" since this particular tester usually uses those. My client is under a physicians care for many things including addiction. I have asked him to get his health care provider to clarify why he would show positive for benzos but.........
Any preliminary test should be confirmed using GC/MS. It is possible, even likely that she has been prescribed a benzodiazepine, either recently or in the past, examples include valium, xanax, ativan, Klonapin, temazepam. These are typically prescribed for anxiety, to prevent seizures in alcohol withdrawal, for sleep and to ease muscle spasms in withdrawal. It is also possible they were prescribed in the past and she used the left over pills to self medicate during withdrawal, or during early recovery. These are also common drugs of abuse and it wouldn't be unusual for someone struggling with addiction to buy these illegally. She should obtain an accurate prescription report from her pharmacy (or pharmacies) most will provide a detailed print out or offer printable versions online. This would not be considered a false positive, but if it is the result of a prescribed medication it is from legitimate use and should not be held against her.
Good luck to you both, take care, Christy