Intriguing story, sounds like it will be such fun. Not a regular cat and mouse story, that's for sure! :-)
I'd work on the logline some more. Just a few edits on the current version: When Mouse, the smartest girl in school [delete the comma] and social outcast [add comma] falls for the head cheerleader, Kat Sanders;[use comma instead of semicolon] She [should not be capitalized] will have to pull every trick in the book to win her, [delete comma, use period] the only trouble [is], Kat doesn't even know mouse [capitalize] exists? and likes boys.
It will then read as:
When Mouse, the smartest girl in school and social outcast, falls for the head cheerleader, Kat Sanders, she will have to pull every trick in the book to win her. The only trouble is, Kat doesn't even know Mouse exists? and likes boys.
I hope that helps.