Why is it controversial for Ophelia to be given some form of Christian burial?

In the play 'Hamlet' (which is what I presume you are referring to), Ophelia's death is generally considered to be a suicide. Many are unhappy with the church allowing her to be given a Christian burial, because in much of the Christian tradition those who commit suicide are said to go to Hell after death. Thus, a Christian burial is usually reserved only for those who died of external causes.