Elizabeth knew of her sister's fear of her, and in pretending to be sick when Mary ordered her to London, Elizabeth was showing the wisdom and cunning that would serve her so well as a ruler. By prolonging her absence from London, she gave Mary's temper time to cool after Wyatt's Rebellion, and perhaps escaped death.
While Mary was dying, why was Philip trying to marry Elizabeth, and why did he want Mary to be kind to her Protestant sister? The reason was that Philip supported Elizabeth over the Catholic Mary Stuart, who he knew would ally with Spain's competitor France is she came to power in England. Philip was correct in that Elizabeth would never ally with France, although she would threaten to do so in later years as a negotiating tactic.
In her early years of consolidating her power, Elizabeth proved her value to the nation with a prudent religious settlement in 1559. Although officially outlawing Catholicism, the law was very tolerant by 16th-century standards. It allowed Catholics to avoid the obligatory Protestant church services by the payment of a fairly small fine. The holding of Catholic masses was technically illegal, but was rarely prosecuted, though it was occasionally cited as a reason for imprisoning political opponents to the Crown. Not very concerned about the religious conflict between Catholics and Protestants herself, Elizabeth's later harshness towards Catholics arose largely because of Pope Pius' interdict, under which all Catholics became potential anti-government traitors. (Despite the papal decree, however, most English Catholics stayed loyal to their Queen.) The role of the papacy in the 16th century differed much from its current form, as 16th-century popes meddled in world political affairs and tried to overthrow governments.