The Celtic Cross is not a Crucifiix; Crucifixes have the body of Christ on the cross.
The note on the desk is the passage from the Holy Bible Romans 14:8, but it is misquoted. The Catholic Church uses the King James translation of the Holy Bible and the correct passage is "For whether we live, we live unto the Lord; and whether we die, we die unto the Lord: whether we live therefore, or die, we are the Lord's." A Nun would not make that error.
When Jessica is talking to Mike Phelps outside of the pharmacy where he works, the pharmacy's delivery van is parked beside a fire hydrant, which is illegal.
The murderer has stolen the victim's habit in order to move around the convent without being discovered. The murderer is several sizes larger than victim, and shouldn't be able to wear their clothing.