I'm so sorry to hear about your situation. It must be hard on you as a parent, and can understand why you feel frustrated, and your daughter is very lucky to have a mum like you
there are many people here who are willing to listen and support, I hope you get help and the advice you need from this forum.
If it's hard to talk to your husband without him getting aggressive, you can get counseling or a mediator/ hospital setting with the specialist/gp and set a meeting with you and your husband on how he can contribute to caring for his child by doing the right thing. Maybe it hasn't occurred to him yet that his daughter has a serious condition and needs proper attention and once he sees the importance of it, he might be able to catch up on dietary and insulin requirements and respond well.
As you said, your daughter loves her dad very much and to stop her from visiting her dad may not be good too. I was a child of divorced parents, and as a child I stayed with my mum on weekdays and my father on the weekends. When I was younger, looking back, I didn't notice neglect or any of the issues my parents had with each other ---I was just happy to see my dad on the weekends. I was too young to understand, but I remembered having fun with my dad on the weekends and any issues they had (my mum didn't like my dad very much said he was irreponsible) I wasn't aware till I was much older (late teens ) and I didn't hate my dad for it.
But if he continues to neglect his responsibilities despite him being taught, then you might want to escalate and call the attention to social services again. Act on maternal instinct, your daughters health and well being is your first priority.
Best of luck to you and your child.