Dear brother, The phenomenon of displaying these sorts of mood swings and blaming you for the loneliness and sufferings are the classic symptoms of SIBLING RIVALRY which is emanating from her inner mind. As a matter of fact, the elder offspring gets a sort of insecurity feeling, when the second one is taken birth since all attention is diverted towards the new born which is beyond the comprehension of the first born. In this context, the child(your sister) construed that she was being avoided by her parents on your arrival, which hurts her in her inner mind.The inner mind of the first child is not so developed at that stage and is not expected to reason or rationalize the core fact. This could have been avoided, had her been given enough attention, care and a reassurance of the unconditional love of her parents in the midst of all your birth and growth. Unknowingly, she displaces her anger towards you which was originally towards the innocent parents. The elder sister, all through her growth compares the love, care, attention, things, events etc which you enjoy that of her and confirms her conviction in her innerworld. These are all the unconscious process started from her childhood since your birth. The lingering thoughts emanated from the harboured emotions are the causes mood swings. Whatever happened has happened. Need not worry. Everything will become alright. Take her to a Psychologist for intervention and for the mood swings, a Psychiatrist can effectively prescribe some medication for a short duration. The psychological counselling and the unconditional family support will invariably help her mind to come in terms with the reality and she can lead a peaceful life.In case you need any further clarification, please do check if you can contact me directly. I am from Erode, Tamil Nadu. Best of luck Great days ahead. Dr Rajesh Thottingal Kalam Rehabilitaion Psychologist from India