Hi and welcome to the forum! I am glad that I can help you.
You want to know the cause of strong smelling urine.
Strong smell of the urine may be caused by increased concentration of the urine due to dehydration or urinary tract infections. Urinary tract infections are characterized by pain or discomfort when urinating, itching in the genital area, pain in the lower abdomen or lower back, pus in the urine or milky urine. There are medical conditions that are also characterized by a changed smell of the urine, such as certain metabolic diseases.
According to the data that you provided, your fiancee may or may not experience any of the medical conditions listed above. She may need to have a bacterial culture with an antibiogram to exclude possible urinary tract infection. She may also need to increase her intake of liquids to avoid dehydration.
Please keep in mind that I provide medical information only. I am not able to diagnose medical conditions. She may consider seeing her doctor for further advice and information about diagnosis and treatment options.