Don't give in! Encourage her to work for her exams for what it will offer for her future. If she doesn't work then, sad though it is, she will learn the hard way. Is there something in which she is particularly interested she can work towards? Has she - or can she - get some work experience that would encourage her? Positive encouragement is far more productive. I'm afraid I don't believe in bribery.
To think that London, or anywhere else for that matter, does not belong to any one demographic