Mary I's relationship with her sister Elizabeth I 

Well Mary did lock her up in the tower of London, and Elizabeth really did think she might get executed by her. Also, Mary had Elizabeth "convert" to Catholicism and had her promise that she would keep England a Catholic country in order for her to succeed her. Mary probably didn't believe Elizabeth's conversion was sincere though and was reluctant to allow her to succeed her, but she had no other option.

She was a good woman :)

U always have to take the good with the bad. Mary resented Anne but was also set in her ways, where Elizabeth was her outlet on anne.

Elizabeth was a horrible sister.