Picture Book with Lesbian main character finds a note, tries to figure out when sent it by handwriting matching

[Katherine]

It's a picture book published likely within the past 10 years about a girl who finds a note in her locker/cubby/potentially valentine box? She tries to figure out who sent her the note by comparing handwriting, and imagines all the different boys who could have sent her the note and doesn't like any of them. She figures out from the writing on her classroom's chalkboard that it was another girl who sent her the note. One of the girls has brown skin and long wavy/curly hair, I think. It is not Love Violet.

[Rainbowheart]

Long shot, The Mystery of the Secret Notes?