You don't say if she felt suddenly dizzy or disoriented or if her leg suddenly went numb. These are symptoms of a stroke.
She may not remember feeling dizzy or numb or anything strange before falling.
She should see a cardiologist.
Wishing you the best
In the UK we get referred to consultants by the doctor, unless we pay to see one privately.
Make an appointment for your wife to be examined by the doctor and explain what happened. I presume that your wife is about your age. There are lots of medical reasons why she may have lost her balance and fell. It may be something to do with her blood pressure or anything.
It is best to make the appointment and get her checked out. Keep an eye on things and also keep a record of this happening as this may not be the first time or the last.
Hope all goes well.
You need to see your physician immediately!