Why is my girlfriend insecure about her big breasts?

How can I make her understand that she doesn’t need to be insecure?
>> Your girlfriend’s insecurity is likely to be deeply ingrained. It probably dates back to primary school when all her friends were still flat as pancakes, but she had already been hauled off to a department store where a matronly shop assistant had pulled a tape measure around her naked chest while muttering about the importance of the “right kind of support”.