Mary had not been happy about the birth of her younger sister, Elizabeth. This was entirely understandable; Mary had been thrown aside, dismissed, her identity taken away from her. Despite a rocky start, there would develop a sisterly love between Mary and Elizabeth. In her youth, Mary had not been an unkind child. After Anne's death Mary seems to have felt compassionate and concern, probably feeling regret that her baby sister was now receiving the same rejection she herself was so familiar with.
The differences between the two sisters, however, were great, and they would become nearly completely estranged as adults.
The beginning of a distance that would mark Mary and Elizabeth's relationship probably began when their brother Edward was king. Their differences were growing, and their personal associations were of a very different persuasion. A clear mistrust was growing between the daughter of Catherine of Aragon, and that of Anne Boleyn. Mary had hardened as a result of a series of miserable occurrences, and she was taking the shape of a sadly unstable person. Elizabeth was sharply intelligent, and also unsurprisingly for a person who had grown up largely without mother or father, was becoming rather wily and resourceful.
The death of Edward marked a time of extreme unease between Mary and Elizabeth, and their relationship as sisters became hopelessly strained.