I have done a lot of research on this and I am also looking for Catherine Mastins parents. This is what I know:
Aaron Mastin (b. 1745) married Rebecca Viele (1745-1795). I have heard the surname Feeley before (not sure if they are the same person but by all accounts she goes by Viele). I know that the only child they had was Rebecca Mastin (1771-1824) and she married Thomas Thomas (1752-1836) so Catherine Mastin is NOT the child of Aaron and Rebecca but I think her parents are somewhere around Aaron's family. I have contacted a genealogist who wrote this: http://www.friendsofsandbanks.org/pec_genealogies/mcd67333.p...
I know that Catherine Mastin married Daniel McDonald. On page 5 of the above link you will find that Daniel McDonald "...married Catherine Mastin #67188, b. c 1793-1795 in New Brunswick? (USA)*, d. 14 September 1879 in Hallowell
Township, Prince Edward County, Ontario, Canada,9 buried in Church of Christ Disciple Cemetery, West Lake.
Age at death shown as 84 on gravestone.
1851 census gives birthplace as "Canada".
Is this person a daughter of Peter MASTIN, sister to Aaron, John?
1871: Widowed, lived with son Robert and family in Hallowell Township"
I'm searching further hoping to find this Peter Mastin link. I'll keep you posted if still interested!