My sister has a psycho fear of injections and she had an appointment tomorrow. Help?

I have an eight year old sibling and all her actions are supposed to be my responsibility. she has to get a vaccine tomorrow, located on the major nerve on your arm personally, I found that horrible when I had the injection as it went so deeply in my sensitive areas, it was hell. Now, my sister has to have the same injection but she has an insane phobia of injections. Last time, she ended up kicking the doctor in his balls as well as screaming so loud that the entire of mexico could hear it. I don't want that to happen again, considering that the last injection was painless. What do I do? save my dignity please...