Yes could be Catholic - it is worth investigating.
I had someone look at the letter and they thought
she was Protestant - I did not ask how this thought
was determined but assumed because of the lack
of any religious context ie. God Bless you etc. The
information posted is all that I know. I have the
genealogy information on her brother James McPhee
born 1758 Inverness-shire Scotland in the Glen Moriston/Glen Urquhart/Strathglass area.
DNA testing has shown that he is not the son
of John McPhee b. 1725 which has been the accepted
line for many many years. Looking for James McPhee
siblings and parents plus more information on his
sister Catherine McPhee MacDonald. It is noted she
signed her letter with Mac Donald but used MacPhee
when he brother used McPhee. Thank you for you
assistance. Do you have any other information on this