I say, until you are ready for her to read it. Our daughter was interested in 5th grade. She, too, is a voracious reader. We decided the content was not appropriate for her at that age and steered her to choose something else.
She read the first one over this past summer (she's 12 now, and in 7th grade). I think it is much more appropriate at this age.
I have not read the books or seen the movie, but I am aware of what they contain, generally speaking. I see it differently than Anne Frank, and differently than some super hero movie as well. It is very different for death to be presented as evil than for it to be presented as part of entertainment.
I would actually be interested in statistics on which parents (at what ages) allowed their children to read these/see the movie and how it compares to which households watch reality TV. It's pretty much the same thing, but upping the ante. Putting people's lives on display as entertainment.
I don't like it. And since my daughter is old enough to understand the nuances of that exploitation, we can have a meaningful conversation about it.
Many people think Golding's Lord of the Flies is terrible for kids to read, because it depicts kids killing each other. But I will say this: At least they weren't doing it simply for entertainment. And it's a neat little study on human behavior when there is no outside authority present, how every society will develop an authority, whether benevolent or not. In the Hunger Games, that authority is what authorizes the grotesque human behavior. Or so I understand.
If you want her to wait, by all means... make her wait. She's your kid.
For age perspective, I will relate a brief comment of my husband's. We have 2 kids, mind you. An older son (who is 15 now) and our daughter who turned 12 over the summer. Husband commented in the spring to the effect that: "I love this age. She is so much fun, and yet still has the innocence. It'll be gone soon and I wish this age she is at could last a little longer."
And it is true. So, while you are musing on how much longer you can hope to keep her innocent, there's a timeline to plug into your equation. Depending upon what you allow her to be exposed to, and what she is exposed to via her friends, maybe around age 12, the innocence starts to fade and they become much more mature in their awareness of the world around them.
Don't rush her through. Enjoy it while it lasts. You/she can never get it back once it's gone.