No, this is not normal- you should get it checked out- the tyre wear should give an indication of the problem- was it general wear, inside or outside edge wear. How much tread is/was left? Is the ESP working? ?Which B does she have?
Fronts on a B will wear quicker as they are the driven wheels.
Obviously it will also depend on your driving style (ymmv), but I would say that tyres on a B should last at least twice that & maybe three times, unless of course your wifes' B is a Turbo & she has a very heavy R foot