Your wife is suffering form dysmenorrheal. It is painful menstruation.
Dysmenorrheal, painful menstruation can start after ovulation till period enters. It basically occurs due to hormones effect. Lower back pain also occurs to some. There is nothing to be worried about. You need to check before all this whether her period is occurring on time or if it's irregular.
She can take spasmolytics like Meftal Spas, which will reduce her pain immediately. She can also apply hot water bag or pressure on her stomach.
If it continues for another week, I suggest you consult gynecologist. Who will do a pelvic exam and USG to find out what's the cause.