Hi,
I'm not a parent but do have some suggestions..
does she refuse to eat because she really is a picky eater?
or is she refusing to eat because she knows it will end in an injection?
To me 4 years old seems like the sort of age when things like that they become more aware of, she has associated eating with injections and testing, so her logice could be that because she doesn't like them, if she doesn't eat she won't have to have that done to her?
If that's not the case and she really is a picky eater, have you tried involving her in making the food? my 6 yr old nephew can be very picky, not that he doesnt like certain foods, he can just be tempremantal in wanting to eat.
I look after him twice a week which involves tea time, sometimes when i ask him if he would like this or that to eat he'll say he's not hungry. When i know that he hasn't eaten since school. So i tempt him into it by saying 'oh well i'll make teddy bear shaped jam sandwiches on my own' ..'what a mess that will make!' ... after trying out a few he usually wants to help and will proudly devour his own messy special shaped sandwich!
As a four year old maybe isn't likely (unless you have a super genius at hand) to make their own meals, it's not really fun for her.. most kids get their food put down in front of them and told to eat it, then if thay have diabetes, they hae to be pricked before hand, then injected afterwards.
Try involve her see if it makes a difference, if you weigh her food, maybe get her to do it, praise her for helping and make her feel extra special for doing so, use some reward charts if you think that would work. It will also be useful in making her aware of food choices etc for when she wants to take more responsibility for her diabetes.
I don't think it's wise to use the whole you dont eat it then you get nothing else. because thats just more negative reinforcement around food and of course you need her to eat so you can keep her diabetes stable.
Hope some of this helps, sorry if i've gotten the wrong idea or anything, just a few ideas as i know what it's like to have a picky eater!!