Good find, Crumblie.
Catharine L MacAndrew died in Edinburgh in 1926, aged 64. She was almost certainly Catherine Lothian MacAndrew, born 1862 in Edinburgh. She seems to have been an only child.
In 1891 she was in Newton Abbot, Devon, with father Donald M Macandrew his wife Agnes B Macandrew, both born in Scotland. In 1881 they were in Torquay and in 1871 they were in 17 Regent Terrace, South Leith, Donald aged 51 and described as retired corn factor, born Edinburgh and Agnes as Agnes Rose Macandrew, 40, born Perth.
Agnes must have been Catherine's stepmother because there is a newspaper marriage notice in the Paisley Herald and Renfrewshire Advertiser on 26 November 1870 of Donald M Macandrew Esq to Agnes Rose Johnston on 22 November 1870. SP has this as D M Macandrew, and also a marriage of D U Macandrew to C H Lothian in Liberton in 1858, and there is a death of Catherine Helen Lothian or Macandrew in Liberton in 1862.
The 1881 and 1891 censuses would explain how Ellen could have got so far from home.
Donald died in Newton Abbot in 1893, aged 73, and Agnes Rose Macandrew died there in 1898 aged 68. The probate of the will of Donald Munro Macandrew, formerly of Leith but lately of Kilrock, Torquay, was sealed in Scotland on 10 June 1893.
That probate was granted at London on 1 June 1893 to John Lewis Macandrew, Captain 3rd Battalion Black Watch and Henry Augustus Johnston, stockbroker. His estate was valued at £34,454 1s 2d, which is equivalent to £4.5 million today (depending on which inflation calculator you use).
So if Miss Catherine Macandrew was Donald's only child she was certainly not short of a bob or two.
Interesting that their house in Torquay was called Kilrock. That is how the name of the ancestral home and family seat of Clan Rose, Kilravock Castle, is pronounced. So was Agnes perhaps connected with the Roses of Kilravock, notwithstanding being born in Perthshire according to the 1871 census? Not that that is of any particular relevance to your search for Ellen Cornish, but it might be of interest.
I note an Ellen E Cornish, aged 25, born Exeter, a housemaid in the household of Leonard Lees in Paignton in 1901, along with Alice Cornish, 31, parlour maid, also born Exeter. If this is your Ellen, it suggests that she cannot have stayed for any great length of time in Edinburgh, because presumably Miss Catherine remained in Devon until her mother's death in 1898, and Ellen was back in Devon by 1901. Or Ellen didn't go to Edinburgh until after the 1901 census, and was back in Devon by 1903.