I understand your concern towards your sister. Depression that too in adolescence needs to be evaluated in detail by a psychiatrist so that the dysfunction caused can be reduced and her quality of life will improve. Information regarding her sleep, hunger, energy levels and concentration at whatever she does would be more helpful to decide on the severity of her condition. However it is easily manageable with appropriate treatment. Some counselling sessions and if needed medical help might be useful for her. I would also be more than happy to help you with that if you are looking for online assistance. Discussions will be held confidential. You can directly consult with me through Practo as needed. Online chat consultation is also available.