Unfortunately for her, the MC inexplicably refuses to make contact with her. She also has an identical twin brother, and while growing up, she witnessed her twin bro laugh and play with the MC on a personal level. As a result, she literally has an "it should've been me" mindset. She is so touch-starved, she projects herself onto her twin bro when he does simple interactions with the MC. I think her mental stability cracked when her twin bro confessed his crush on the mc. So, in order to getting BSS'd by her twin bro, she BSS'd him first; she confesses her love and dates the MC.