Hi thanks for your question.
6 years old and weight of 130 pound means morbid obesity
. The hump at the back could be collection of fat and there is nothing to worry for this hump. What she needs urgently is control of this morbid obesity. She should be investigated to rule out any metabolic disorder like hypothyroidism
of tummy is expected with this much of obesity. With so much of obesity at this stage of life can have lot of health related problems in her feature life. I would suggest you to consult an internal medicine specialist preferably an endocrinologist
who may evaluate her for such a morbid obesity and may advice you a management plan.
Hope this answers your question.