While this type of thing could be upsetting to you, resist the urge to interrupt. The experience could have frightened your child, and this is her way of re-enacting the situation and possibly getting over her fear by being in control of the situation.
If you notice a particular scene being played repeatedly, join in the game and encourage your child to think about what she is doing. For instance, those teddies that are having countless injections - ask your child if the teddies are sick or if the teddies are happy or sad.
If your child tends to include violent themes in most of her play, check what it is that she is seeing on television, or whether she is perhaps being exposed to some sort of violence in real life. There is a risk of preschoolers becoming adversely affected by the news, cartoons, or movies.