You are Stiles’s older sister, and more recently- Derek’s newest beta. Though it seems the two of you have a connection stronger than he does with his other betas… you went to Deaton for help figuring out why, and he revealed that you are sired to Derek. An alpha who had feelings for their beta prior to turning them, will result in the beta wanting to do anything to please their alpha as long as the feelings had been reciprocated prior to them turning.