In Hamlet, explain the gravedigger's bewilderment when he asks, "Is she to be buried in Christian burial?" What is the issue?

The isse at hand is whether or not Ophelia deserves a
Christian burial in light of the rather suspicious circumstances of her death.  If
Ophelia willfully committed suicide, then she committed a murder (of self), and
therefore committed a mortal sin which the Catholic Church would say precluded her from
being buried in sanctified ground.  Suicides where generally buried in a field or at a
road-side -- someplace suggesting the lack of dignity of the act of
suicide. 

Because Ophelia drowned, the question is: did she
drown herself or was it an accident? The gravedigger explains it as
follows:

If
the man go this water and drown himself it is, will he, nill he, he goes.  Mark you
that.  But if the water come to him and drown him, he drowns not himself; argal, he that
is not guilty of his own death shortens not his own
life. 

Because Ophelia shows
clear signs of craziness and the description of her death suggests that she didn't try
to save herself, she merely let herself sink, it is likely that she did, indeed, kill
herself.  But because her father was Polonius and she is close the king's family,
Claudius probably intevened with the law so that Ophelia's death would be ruled an
accident.  This move would save her reputation and keep Laertes under Claudius's
control.  The loss of both his father and now his sister could drive Laertes over the
edge, and Claudius needs him to fulfill their plan against
Hamlet.