Children should not be beaten at all. It does not really help with the cause of the problem.
I think the child knows that there are different rules from grandparents and parents, and she is trying to get her way all the time. The mother will have to learn to discipline the child by raising the voice or depriving her of a favourite activity or privilege. If the grandparents are setting up some rules, they will also have to help in handling the child's bad temper.
Find out why the child is frustrated or when she becomes stubborn. There must be a cause for everything. Pay proper attention to the child's diet. For example, no extra sugar, no market made fried foods or Cola drinks.
Cut down the hours of the child's TV watching. Select the programmes that she views. Make sure the child gets enough sleep and rest and that she has some quiet activities as well.