I agree.
AFAIK, even insulin-dependent diabetics can experience low blood sugar, it is just rarer than experiencing high blood sugar. So it might not matter. If she naturally went into a low-blood sugar, it's possible he just left her there without seeking medical attention and she died. But that could never be proven at this point. Sometimes even when you do give them sugar, they can be too far gone for that to help at all, though evidence of that could prove that he tried to help but again - impossible now after all these years to determine that. If he was in a different room, it can be hard to hear anything has happened at all.