After Mary saw Treena's picture in the paper and she called her on the phone, she identified herself as Mary Shepherd, not Mary Shannon. Have I missed something along the way or is this a goof??!!

I was wondering about that too. I can't even think of a good reason for it, so maybe it was just a boo-boo?

I think she uses Mary Shannon as an alias, she needs to keep herself on the low low, that was my take anyways.