I think dogsbody has a lot of good points.
The potential hacker romance sounds like a secondary plot thread, something you could just leave out of the query.
Marija's disappearance and the crazy extinct language emails sound like the most important incidents that move the story along -- but I could be wrong about that. I'm having trouble sussing out what the connections between events are, though the different pieces all sound compelling to me.
How much time passes between the disappearance of her friend and the mysterious emails? I kind of want the emails to come early in the query, because they're cool, but it sounds like they actually come later in the story.
Could you do something where you start there, like...
- Cristina is doing her hiding-out-at-home horse chat room thing and then she gets creepy emails in extinct language
- she's got to crack the code because maybe
- the emails could help her find her missing friend [brief missing friend backstory]
- or provide a clue about her attacker [brief attack/husband backstory]
(actually now that I think about it this seems implausible from the info you've given us -- if her husband is just trying to get her out of the way because he has a new girlfriend, why on earth would it involve emails in proto-indo-european? but of course I don't know all the details so maybe it makes sense.)
- something something race against time further explanation of stakes?
Obviously the above sketch leaves some things (all things) to be desired, but I'm just trying to play around with possible query structures. Will keep thinking about it.
Thank you for the thoughtful comments. The attack, Marija and the emails happen in the first two chapters. The only backstory is the husband leaving. The girlfriend and baby are in the first chapter, too.