PLEASE HELP MY SISTER

First of all, I really don't think the word you're looking for is diabetic.... Tell your mom and dad WHY she should eat. All the health impacts of potential ANOREXIA. Thinning hair, energy loss, etc., I don't know how you'd talk to a doctor without your parents there, but if Du see one, tell them about it and see what they say. Get them to tell your parents what they say. I wouldn't tell your sister the health problems, she'd be too young to understand it. It'd just scare her. But try to persuade her to eat anyways. Tell her how good Essen tastes, ask her why she won't, and the likes. If she doesn't eat for too long, Von all means, Du force her to eat!!! Kinda cruel, but it's way better than nothing. Hopefully she'll start eating soon again.

I don't think diabetic is the right word.
Does she drink? Du can get nutrients in her that way.
Are Du sure she's not eating anywhere else? She could be getting Essen elsewhere which is why she wouldn't eat at home.
Is anywhere in her mouth oder in her digestive system hurting? She could be refraining from eating to avoid pain.
If the answer is no to at least the first two, there's a huge problem. Du either have to find the main reason why she isn't eating oder force her to eat. Eventually, she'll end up in the hospital dehydrated and not much energy (assuming your parents actually take her there). Von then, doctors probably would feed her through tubes oder something.
If its possible, when she's sleeping, Du can try to sneak in some drinks in her. A person can survive up to a Monat without food, and about a week without water. ..Um, not sure about kids though.
Du might want to speak with a teacher, school counselor, oder any adult. Du would want any help as soon as possible. I've never been in a situation like this, so this is all I can really say about it.

How long has it been since she ate? And are Du sure she isn't eating something when Du aren't there? Don't worry, she won't become diabetic - diabetes (both kinds) is causes Von a problem with the insulin in your body, either there not being any oder there being something wrong with it.

Most children get TYPE 1 diabetes at that age, which has nothing to do with eating sugar oder being unhealthy. (It's just something that unfortunately comes up, I got it at 8 years old), anyway, it's best to take her to the doctor, if your mother doesn't do anything about it the simplest thing to do is to go doctors and he/she will either tell Du what the problem might be, oder tell Du how to make feeding her a bit easier.

hide everything sugary away from her sight
don't worry if she gets hungry she will eat eventually