Constantly terrified. Any advice?

8 months ago my partners child was diagnosed type 1 diabetic. A couple of months later I was shown how to do her insulin injections and how to test her blood sugar levels, told rougly what to do when she was low and high and then asked to babysit alone the next day. I now look after her 2 days a week and am constantly terrified! I don't understand diabetes, I mean I know the pancreas stops producing inslulin and all that but in many situations I don't knows what to do. I try asking my partner for help and telling him how scared I am but he gets annoyed, thinks I'm totally stupid and It starts an argument.

I've started to go to a childrens diabetes club with her with the hope of learning more and possibly try find someone there to help me but they all treat me as if I'm stupid and have been cast out by them. They have long conversations about different types of insulin, about pumps and carbs and I have no idea what they're talking about. While they were having one such conversation about carbs and I mentioned that I never knew about carb counting and that my partner doesn't do it, their jaws practically hit the floor.

My partners child constantly has high blood sugar levels but is always hungry, I've been told not to give her food if she is high and to get her to exercise but she often cries saying she starving hungry and I feel terrible. In so many situations I have no clue what to do and I'm terrified one day something will go wrong but noone will help me and everyone expects me to just shut up and get on with it.

Thanks for replying! I know how to do her injections and test her blood and everything but as I have no understanding of the way her body works and the reasons behind everything I feel like I can't ever learn what to do unless I understand diabetes. Like what to do when she is hungry but is high or bordering high, what to do when she does lots of exercise to stop her going low ect... I understand how to deal with highs and lows but not how to prevent them, actually I don't know how to deal with highs, other than being told to get her to run around or give her an extra Insulin unit with her meals but outside of her meals I'm clueless. There's a million other situations I'm completely clueless in and I feel terrible, like I'm putting her in danger for allowing her to be in my care. Does anyone know if there's any organizations, Healthcare professionals or courses I can do to learn more?