Going back to the original point ( sorry I hadn't read this before) The little girl in the film refers to Nessie as a Kelpie because there is a story that St Columba battled with the Kelpie at the Fort Agustus ( I don't think that's how you spell it ). This is at the west end of Loch Ness. If you ever get a chance go and visit its wonderful area of the country.
On another note one of the sixes (small groups) that Scottish Brownies ( small girl guides) have is Kelpies. I was a Kelpie when I was 7-11.