Hi Anne
I'm afraid, with respect, I cannot agree with you that Sarah Margaret made up her fathers' name. Firstly I can't see why in her first marriage ( Aged 15) she would not acknowledge a father other than that his family were still alive in the area or perhaps even at that age she did not know his name.
Secondly where she acknowledges him as Charles in her second marriage she is aged 53 and he is probable dead.(even if the death, in 1895, of the person I THINK is the Charles is incorrect). Also she is not a child looking for a father at that stage.
Lastly in the Griffith valuation for the Townland of Ballyvennox in 1859 has a CHARLES renting ground from a Thomas King (the name of the father of David King, father of Sarah Margaret's older half sister).
One other thing is that Ballyvennox is very close to Adverness where S M lived aged 15.
This is all very complicated but for these reasons I am inclined to believe Sarah M's father was a Charles and not only that she said in her second marriage cert he was not only Charles but Charles Pollock.
Without further information I will probably never be absolutely sure but I do thank you for your interest and input.
Doire.