long story drama: am i overreacting?

so this girl in my grade has liked my boyfriend for the longest time ever. she's always trying to be lowkey about her liking him and she always denies it but she gives him hand written letters, tries to get his attention, join clubs and teams he's in so she can spend time with him on purpose. she's being really annoying lately and we consider ourselves "halfies" cus she's my other half, like a really good and close friend. however, last night at her birthday, she asked to take pictures with him and fyi, i hate her guts cus she thinks that just cus she's single, my boyfriend is single too. like bitch no! so she wanted to recreate this pic from her bday last year which was just then standing. but this year, she took photos with him, hugging him, leaning her head on him, her arm around him, it pissed me off so much! before the party, i told him he could take the pic but tell her not to post it and she did 3 hours later at her party! my babe told her to take it down cus you don't know how pissed and jealous i get cus i know what she is capable of! but she replies to him, "it's my birthday i get to do what. want" and even the next day she says she wouldn't do it and have I mentioned, she hasn't even deleted her last pic of him and she had so many boyfriends and never posted them but yet she keeps the one with my fucking boyfriend. 2 photos now. and also my whole grade dislikes her cus she played most of the guys and she's really rude so everyone's okay with me starting beef with her.