Freud at Work

I work with this very nice, personable young woman at work. Lately we have had long shifts together leaving a lot of time to talk and get to know a bit more about each others' lives. I find her mentioning her brother over and over again in all of our conversations and I can't help but think she has this very strange attraction to him. She buys groceries for him, takes his picture for a photography project, helps him excessively with his film class assignments, and spends large amounts of time with him. If a father figure isn't present, can an older brother act as a replacement for the daughter's supposed unconscious attraction to her father? If a mother figure isn't present, can an older sister act as a replacement for the son's supposed Oedipus attraction to his mother? I find the same attitude of my best friend and her older brother. Her father got cut out of their lives as young children because of alcoholism. She seems overly-attached to her brother and really tries to make him happy and always begs for his attention. I have an older brother and I don't find myself trying to hang out with him or do unnecessary errands for him. I love him and if he asks for my help, I am always going to do my best to help him but I do not desire his attention constantly. My parents are not separated and my dad has not always been the best father but has always been present. I wonder if this attraction can apply to siblings if the parents are not around.