From Sister Mary's personal point of view, at that time, Father Henry and most people in England advocated Protestantism and rejected Catholicism. As a loyal Catholic, Sister Mary suffered humiliation and pain from childhood. The religious struggle serves politics, and Mary is the victim of this struggle. Therefore, it is understandable and natural to liquidate Protestants after Mary came to power-because Protestants have persecuted Catholics in the same way before.
Therefore, as for the form of burning, it is a way and a tradition that Catholicism has always adopted in dealing with pagans. From this point of view, it is not cruel for Mary to burn pagans.