I have a unique question here, its really about weight, so I have a cousin who is a female she is 16?

and weighs about 290 which is the same weight as my 12 yr old sister but anyways the thngs is though my 16 year old cousin has health issues that makes her gain weigh rapidly then lose it at an even faster weigh. within the last 4 years she has lost and gained then lost again 250 pounds. doctors have monitored her weight lost and weight gain due to the fact she has type 1 diabetes which she had since age 3 and she has hypertension and hyperthyroid and she has sickle cell, my main reason question really is how do you think she can lose weight and keep it off? now let me also mention she does not over eat, her parents have surveillance cameras in every inch of the house so we know she doesnt over eat plus she has a personal gym at home and she excercises at least 3 hours per day but still she continues to have these symptoms now the doctors say that its because of thyroid but the thing is though we have had 5 doctors tell us this do u think we need a 6th or 7th opinion?