After years processing her brother's suicide, nineteen-year-old Riley finally has it all figured out: she is lead singer of her band, dating the perfect girl, and is one of the brains behind her university’s experimental memory-erasing device. Then her uncle sexually assaults her. How about: 'Just when nineteen-year-old Riley has it all figured out, her uncle sexually assaults her.' I think the other aspects of your hook can come in the paragraph after. Like: 'She had just come to terms with her brother's suicide. She was the lead singer of a band, was dating the perfect girl and was one of the brains behind her university's experimental memory-erasing device. But the trauma from her rape turns her world upside down. (Or something like) Your original hook is good - but I agree with others that it feels too long.
When the trauma from her rape tanks her relationship, Riley seeks a fresh start. She leaves college and takes up a tutoring position at a music class. There, she is assigned to eighteen-year-old Luke, a music savant plagued with composer’s block since his mom’s death.
As Riley aids Luke in reigniting his creative spark, the two start a romance. But when she discovers Luke’s involvement in her brother’s death, Riley feels betrayed again I think another word other than 'betrayed' might be better - like 'horrified' maybe. Now she must decide whether to use the device to wipe her mind clean of all painful memories This comes across as quite abrupt to me - maybe before it, you could add a sentence about her desperation to forget everything, even though it could erase her entire identity.
THE SUM OF WHO WE ARE is a 65,000-word young adult novel, with light science fiction elements, told in Riley and Luke’s alternating perspectives. The completed manuscript is available upon request.
(Okay, so I've been getting a lot of comments about my hook being too long. It's just that all the pieces of info that constitute are relevant. The piece on her being lead singer of her band explains why she's qualified to guide Luke, the part about her dating the perfect girl reveals her sexuality, and the part about her "being one of the brains.." introduces the concept of the memory-erasing device. Let me know if you have any suggestions on how to make it succinct.)
The story looks good and Riley's character seems very interesting. Thank you for your feedback too! Good luck!