Seventeen(-)year(-)old Camria and her twin sister Liz were the first children ever conceived and born on the International Space Station. Hmm. This is pretty good. Not only does it set the scene and build the world quite succinctly, but it carries with it tons of backstory, without having to labor over it. Cam just wants to be a normal high school junior and skip all the attention that goes with being a highly publicized “space twin.” But when she’s blinded in a freak explosion, and Liz disappears, she’ll do anything to get her sister and her sight back. Technically this whole sentence is a clause dependent on the previous sentence. I realize you're doing that on purpose, but I'm not sure a query letter is the best place to play with grammar rules. We'll see what my readers think.
All in all, this open is pretty great. As always, I would like to have a little more characterization for Cam, you know - what her personality is like before her story begins, but this opening is pretty strong without it.
Cam suspects there’s something more to Lander, a new transfer student, than his odd accent and his interest in her. The sequence of this sentence reads a little awkwardly to me. Maybe start with Lander, his accent, his interest, and then finish with Cam's suspicions? Turns out he’s from a planet not yet discovered by Earth, and he knows why Liz disappeared. A high-tech alien faction So Lander is not human? It seems to me he must not be, but you could probably make that clearer. is bent on taking over minds of unsuspecting humans, and they've started with Cam’s sister.
Okay, as substance goes, this is good. We've got clear conflict, high stakes, and a character that could be either a romantic interest or an antagonist, and that's all pretty good, but the execution here feels off. For one, the voice feels a little dry, and for another one piece of information doesn't feel like it leads logically into the next. I hope that makes sense. I realize that in a query letter, you don't have room to always link everything together smoothly, but I think you should think about the order in which you present things, and make sure you're giving your reader enough.
When Lander offers to take Cam to find Liz, and to restore her sight with his advanced technology, Cam accepts, but whoa. She didn't count on traveling through wormholes, fighting off mind control, and facing her own growing attraction to Lander. After Lander appears to turn traitor, How? Cam must decide to cut a deal to save her sister and herself, or risk their lives to keep the enemy faction from stealing more minds from Earth.
This is pretty good, too. You've certainly got a decently sadistic choice here, and it leads to clear consequences on either side. My one gripe is for you to get specific about Lander's turncoating. Always try to be as specific as possible in a query letter. Vagueness only makes your story look like so many others. That said, if it's super complicated what happens in the story, it can be difficult to fit it in a query letter. You have to use your best judgement about what to share and what to hold back.
I also think one more thing you need to make clear is whether Cam gets her sight back. If Lander ditches her, and she goes through the whole book blind, that would be one kind of story, but if she lets him restore her vision first, that is really a completely different book, you know?
STARTRIPPED This title seems weird. Could you maybe hyphenate it: STAR-TRIPPED? is an 85K word
In summary, this query letter is really pretty good. You've got Conflict and Choice down pat, and you've got a decent start to Character, since you open with your protagonist in a situation which sort of automatically characterizes her for us a bit, but you could use a little more.
Then, I think it's just a matter of rearranging a few things, and spicing up the voice a little. You've got one "whoa" in the final paragraph, and that was the first time this query felt like it was written by, about, or for a young adult. One exercise that can help with voice, I find, is to write the query from the first person point of view of your protagonist, and then edit it back into third person.
What do you all think? This query is pretty close, isn't it?
P.S. Today is also my day to post over at Project Middle Grade Mayhem, and I've written a bit about why my family's vacation next week means so much to me.