My Mother Recently Took A Urine Test At The Doctors

My mother recently took a urine test at the doctors office and tested positive for meth and amphetamines and did not test positive for her oxycodone hcl..I seen her take the meds before we went to the appointment. Can medicines such as trazadone and ranitidine cause that false positive for meth? And why didn't her oxycodone hcl show up? help!