About 6 months ago she suddenly started dropping weight. Extreme exhaustion (winded after going up a flight of stairs), dropped 30 pounds in two months, she was starting to get skeletal. Still not being active with her healthcare, but when she went under 110lbs for the first time since she was 14, she finally found the motivation she needed to get proactive and quickly found a better team of doctors who diagnosed her with Type 1 and put her on Insulin immediately.
Today we're putting her 2nd Omnipod on her for insulin delivery. She should get a closed loop system soon, I guess the iPhone support for her Omnipod+Dexcom combo is still going through FDA approval. Her new team says she's lucky to be alive at all. They've been going through her extensive medical history, pointing at occasions when she was hospitalized during her menses and saying "here you were going through diabetic ketoacidosis, that's why you were vomiting constantly", "every evening you're going critically low, that's why family thought you were a closet alcoholic", and "on average during the day your blood glucose is far, far too high, that's why you drink and piss gallons of water per day but are never sated".
So... I guess yes you can get lucky and survive, but with symptoms strong enough that it _should_ be caught.