....and a bit more:

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1841

FARGHER Catherine 23 Castletown 1464/5 46 12
FARGHER Catherine 21 Castletown 1464/5 24 10
FARGHER Catherine 20 Castletown 1464/5 4 2
FARGHER Cathrine 20 Malew 1464/4 12 17

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Looking these up in the 1841 census and eliminating the “wrong” ones:

The 23 yr old was Cath Fargher nee Sayle (m Wm Fargher 1835 Malew --- she was from Rushen, under age with consent of her parents)

The 21 yr old was the daughter of Richard and Harriet Fargher.

The 20 yr old in Castletown was a servant on Parade, in the household of a Government Chaplain with his children and several boys from England --- looks like a small boarding school ? This is a good candidate for your Cath Fargher.

The other 20 yr old (in Malew) was at Little Scarlet
John Fargher 65 farmer
John 35 lead miner
Robert 25 shoe maker journeyman
Elizabeth 45
Catherine 20
Jane 15

Since the relationships weren’t given in the 1841 census, it’s impossible to know for sure whether this could be your Cath with (eg) uncle/grandfather. Someone might recognise this family and know who this Cath was.

Jean C