Girl Drama

I know this is super common & dumb but I need to vent. why is it that girls just like to start drama or get mad for no reason?? I recently added an old friend on IG and she just denied my request and it's so stupid cause I've never done shit. her boyfriends best friend went to my college and whenever she would come I would be so nice offer her a place to stay with me for the night & all.. randomly find her on social media, social media now a days is everything so I don't get why some girls hold bad blood. whatever she was always up and down with me but last time I saw her was my freshmen year and I recently just graduated I sound like a pissy biyatch but if girls would get along I swear we would rule the world.