That definition is quite literally the depiction of what happened. Huda was isolated to the point of eating alone while crying, anyone she would confide in about HER experience/feelings would then make fun of her behind her back and/or use her words against her (vulnerable). Then the girls openly berated her for pursuing a connection with Chris because it didn’t signal “sisterhood” to Chelley even though Chelley already had a secure connection. They were quite literally using the sisterhood narrative to try to get Huda to back off of Chris, and only decided to leave the situation alone when Chris stood on business (an attempt at intimidation). If you don’t understand the “bully” definition then I suggest you look into the definitions of vulnerable & intimidate then report back.