Karma for posting, Rachel!
Right now, I think you need to find a bit more focus. I'll take a stab at it....
Sixteen-year-old Catalina Bramson loathes mucking manure out from the pegasus’
stall at her parents’
---> feels a bit clunky. Could you just say 'where she works?' The fact that her parents own it doesn't feel important. Myth Rescue Center,
but fleeing murderous mages isn’t the alternative she pictured.
This complicates things, I think.
Harvesters—people who harvest body parts from mythical creatures to gain magical powers—are the reason Catalina spends her time nursing maimed Myths back to health. When a mortally wounded unicorn arrives at the center, it passes on a coded message with its dying breath, cat
apulting --->maybe a different word since you have 'cat' twiceCat
alina into danger. Now, the Harvesters are eager to put her into an early grave for knowing their plans. How did they find out?
They intend to corrupt the magic binding the world together to reshape everything under their rule.
Enlisting the help of her dying boyfriend, Catalina must find a way to stop the Harvesters. Catalina learns a secret though. ---> She just learned one above. Not that she can't learn two, but, somehow this feels too much.
She’s the reason her boyfriend suffers from a fatal illness. ---> This feels like a whole new plot.
If Catalina wants to prevent the Harvesters from destroying everything she holds dear, she’ll have to betray the boy she loves to do so.
---> This end hook doesn't work for me, somehow.
Right now, I feel like these are almost separate tales. I'm sure they're well-blended in the story, but it's not coming through in the query. A couple of other things: what does the MC want? Things are happening TO her, but she comes off a bit passive. And what are the stakes? Betraying the boy she loves to save the world? That just doesn't seem like enough. She can always go back and beg his forgiveness.
Not sure if this helped, but I hope it did a little!