Something has to be wrong….it’s just not normal for a dog of that age to be constantly *********. My female Doberman was holding her urine all night by about 4 months old. Hurry and get that check for diabetes…..something has to be wrong medically if you are consistently doing everything you have mentioned. Dobermans in general are very easy to housebreak so this sounds very alarming.
Sorry, I don’t know what to tell you other than to keep looking into possible medical causes and continue training as you have been. It sounds like you are doing everything correctly.

I would normally tell you to restrict water during certain times, but in a dog that is even suspected of being diabetic, that could be dangerous. Rule that out first and then see if restricting water intake to certain parts of the day helps. Not giving any water several hours before bed can help the overnight situation and only giving water at certain times during the day when you can be letting her out afterward is a good way to control it during the day.