The ones I got her are: Starship Troopers, Rolling Stones, Have Spacesuit Will Travel, Podkayne of Mars, The Star Beast and The Moon is a Harsh Mistress (still debating on that one - might not give that one to her).
BUT, based on your recommendation - and because I trust you wouldn't choose something inappropriate - I just bid on Ender's Game on ebay. I wasn't going to spend anymore... but... :-) books is worth it! :-) She's getting much more from me than any other niece or nephew with just those. Somehow, I feel too much empathy for her to *not* let her be a favorite this year. :-)
Wait for a year on "The Moon is a Harsh Mistress". It is a wonderful, wonderful book, but at her age she might get distracted by the weird marriages (clan, chain, line, and other polygamous structures) and the light sex. Read it for yourself, if you haven't, and decide when she'll be ready.
I would urge caution on "Starship Troopers" but... that one's only going to instill a rabid love of those who put their bodies between us civvies and danger, so what's the harm? And "The Star Beast" is great. It's still a favorite of mine... has some of the best characters. Lummox, and John Thomas Stuart the whateverth, Mr. Kiku and Beulah Murgatroyd and Piggy-Wiggy... "Have SpaceSuit" is good, it might just inspire her to start learning on her own (it did me!)... oh, you have good taste.
Ender's Game is recommended because one of the messages - if you're ignored, what you do is make them unable to ignore you by being the best there is - is so true for a troubled kid. And she'll never, ever wonder if there's an "up" in space. "The enemy's gate is down".