I fully agree that we should be very careful about casting aspersions against anything to do with the Church. There are plenty of non-Catholics out there gleefully doing just that already. As Catholics, we should defend our beloved church, priests and nuns as much as possible.
However, bad things do sometimes happen within the Church–even by nuns and priests. An example of this is the pedophile priest scandal. A priest abusing a child is always wrong and creates a scandal when and if it’s discovered. However, the REAL scandal that occurred and that all Catholics still are dealing with the reverberations from, was the lying, cover up and transferring of priests to hide what they had done. If the nuns at this convent committed atrocities, it needs to be investigated, admitted to, and apologies and some type of atonement carried out—along with serious changes being put in place to assure that something like this never happens again.
If we just blow the accusation off without at least giving credibility to the fact that an accusation has been made, then we fall into the same trap that church hierarchy did with the pedophile priests scandal! (ie: Deny, deny, deny) I don’t think that is what Jesus expects from His church!