Actually most diabetics are perfectly fine. The cases you see on the news are people who never went to the doctor and thus their levels were out of control for a long time (usually decades), or people who are terrible patients and will never administer their medication properly.
Advanced diabetic retinopathy (the point where your vision is significantly affected) you will typically only see in older patients, as it takes a very long time to actually occur. At Amber’s age she probably just had myopia, and the stye is probably what it is or some minor infection from never washing her makeup.
Still, she should probably get checked for diabeties. You can still treat patients her size, though the heavier you are the more insulin you will require (typically, there’s some edge cases). But it’s better than being sick all the time.