Yes ,you seem to be absolutely right.
You will produce large amounts of urine, usually more than 3 - 15 liters per day,if you are suffering from diabetes insipidus
If you do not drink enough fluids, dehydration
can result,resulting in low levels of potassium.
Other symptoms of diabetes insipidus are
,rapid heart rate
,irritability,fatigue,lethargy,muscle pains etc.
The symptoms of deceased girl matches with classical diabetes insipidus.