There are a dozen people named 'Cathel Kerr' listed on Scotlandspeople in the 1841 census, ranging in age from 10 to 60, and the name only comes up in the one small place of Assynt, even if you search for the name in the whole of Scotland.
A couple look as if they could be the Cathel baptised 1802, but I don't have any credits to look at any of the records to see if you can find out.
Of course, they could be Cathels born to other members of this Kerr family, who also used the name.
It's going to be quite a jigsaw to find if indeed your Cathel did come from there!
I did see on a search around on familysearch, reference to a book 'Population lists for Assynt 1638 - 1811' by Malcolm Bangor-Jones. Published 1997.
It seems to be a book(let) in their main library - I'm guessing Salt lake City. Not digitised and not even on film, so unless you live anywhere near Salt Lake City, difficult.
It does suggest you go to World Catalogue to see where else there might be a copy.
You might be able to track one down.
(I've just done this and found they even have one in the Research section at the Central City library
here in New Zealand! Only in-library use.)
It evidently has population lists for 1638, 1667, 1691, 1746, 1774 and 1811.
Might prove interesting, although I'm not sure how much information it would give you.
If you Google this title, you can read more information about it - written by Bangor-Jones. (It's the 'Introduction' from Page 1.)
Malcolm Bangor-Jones has also written a book about the Assynt Clearances. Also on familysearch
If you Google "Assynt Clearances" you'll have lots to read!
Malcolm Bangor-Jones has a website offering genealogical research. He seems very knowledgeable about the area.
If your Kerr family did come from there, looks like they got out just in time.