After the death of her best friend, a teenage girl begins to notice and investigate strange inconsistencies in reality, attracting the attention of a dangerous organization.

“After the death of her best friend, a teenage girl must battle a dangerous organization that wants to wipe her memory when notices strange inconsistencies in reality.”

…or…

“When the death of her best friend causes a teenage girl to notice strange inconsistencies in reality, she must battle a secret organization that seeks to wipe her memory.”

Hope these help. They’re more active than your initial version, and also give the protag a goal to achieve and reveal what she’ll lose if she fails. By showing the protag’s goal and the stakes in the logline, a reader will get a better sense of what your story is about and how it might play out on the page.

I like your concept. Think it might have legs. Best of luck 😉