My guess would be that she saw something on tv or read something that triggered this image. But what you need to do is to simply....
Talk with her. Like "wow, what a picture! So much is going on. Is the guy ringing the bell happy or sad?" "Was there anything that you recently saw that helped you draw this pic?" Or something like that. Main thing is just to talk with her. And no I don't think you should find this disturbing. If a boy had done this, there would have been tanks, guns, etc. Oh, was the pic in color or black and white?
Oh, and if you don't mind....we would love to know what the inspiration for the drawing was.
So your daughter imagined a scene and drew it like one would if they were to write a book. It seems that she is capable of more complex scenery than others her age, at least in her class. I'm not sure this is a bad thing. From what you've described in this picture, your daughter is able to see the connection that man is a beast like any other, that our lives are temporary, that our bodies provide mean as any other creature for the vultures (which are common). I would think that, if it were my son, that he was an artist that was able to allow his imagination to flourish. I think it's a good thing. It seems your daughter may have a gift. If it were me, i would take this as a sign that your daughter is interested in art, and probably take her to a few abstract art exhibitions in order to help her develop her artistry. Please remember though, that there are no rules in a person's artistry and there shouldn't be. That being said, my son copied a well known piece of two men, both holding each others organs for his high school final art piece and we laugh about it now, that at the time i immediately wigged out and told him to draw a picture out the newspaper and not to turn in a piece of "homosexual art". So he copied a newspaper article picture, where a bunch of white men stood around, while one was beating a black man. Both pieces were great, and for both pieces he would received the same mark, an "A". It was my reaction that could have caused him to turn from making art. My reaction and my expectation of what is "normal". I'd hate to think that i stopped his creative vision. It is a regret i have.