I am not sure what I should do, as she does not want to go for further tests. Urine retention will usually require further invasive studies to find the cause. This can restore the columnar epithelia necessary for this part of the body. It should be applied twice a day for at least 6 weeks to see if it will help. If this does not help she would be best advised to get further invasive studies.
Drug testing can be quite specific or general.
Screening urine tests will occasionally test positive for other substances. Better drug testing will not-except in very rare conditions. Female urinary incontinence has a variety of causes. However, vitamin deficiency is not usually thought to be one of them. Consequently, taking vitamins wouldn't be expected to help the problem.