Mary and Celosa were colleagues. They worked at the same place. They truly didn't know one another as their work didn't overlap. Mary outranked Celosa in terms of salary and position but in Celosa's mind they were on the same level. Unbeknowst to Mary, shortly after her arrival, her boss and other members of the executive management team had given Celosa the task of "keeping an eye" on Mary. One day Mary's boss slipped up and told her so. Mary thought whatever and let it go.
Celosa was very mean to Mary while Mary just looked at Celosa as another person who happened to be there. A person occupying space. Celosa was fully invested in everything that Mary said and did. Celosa was very disrespectful to Mary yet Mary paid Celosa no mind which made Celosa very upset. Mary would overhear Celosa trash talking her and would catch her rolling her eyes and passing evil looks whenever she would pass by. Whenever anyone new would join the firm, Celosa made it her business to attempt to turn them against Mary. She would gossip, lie and let it be known to stay away from Mary. Mary continued to stay in peace. Mary tried her best to avoid Celosa but Celosa was bold. She would invade Mary's workspace and do all sort of nonsense to elicit a reaction. Mary refused to give Celosa evil self a reaction.