Name, year of birth and death, occupation, from:
https://www.geni.com/people/Ellin/6000000045380393949

Black & white photo found on:
https://www.myheritage.com

Brian of nzolivers.com says a Horneman descendant in New Zealand has a painting of Ellin Devis.

Date of death from this Death Notice from a 13-pager document compiled by, and received from, Julie Bourke (nee McColl) on 27 April 2017. Julie is the great-granddaughter of Emma Caroline Horneman and Henry Gosling Clark:
The Times Thursday 24th February 1820
On Monday the 21st instant in Devonshire-place Mrs Ellin Devis aged 73.

Notice from a 13-pager document:
The Morning Chronicle, Thursday 20 July 1820
Genuine Effects, Devonshire Place, near the New Road – By Mr Squibb and SON, on the Premises, THIS and following day, at 12, by Order of the Executors.
ALL the remaining HOUSEHOLD FURNITURE, Plate, Linen, China, Prints framed and glazed, several hundred Volumes of Books, Five Grand and Cabinet Piano Fortes, by Stodart and other eminent makers, and a great variety of other Effects, the property of the late Mrs Ellen Devis, deceased, at her residence 20 Devonshire-place, Wimpole-street, next to the New Road; comprising a drawing room suite of chintz cotton for eight windows; with sofa and chairs to correspond; numerous bedsteads and furniture, a great quantity of excellent bedding, and other chamber articles, a range of library cases, writing desks, tables, forms, chairs, several valuable fixtures, a quantity of panelled partitioning, various presses, kitchens requisites, &c – to be viewed, when catalogues may be had on the premises; and of Mr. Squibb and Son , Saville-row.

According to the “Devis Family Tree” kindly shared by Julie Bourke (nee McColl) received in the post on 3 May 2017:

1. Henry Devis and her sister Elizabeth Devis b. 1764, were mentioned in her Will. She was a spinster.

2. Ellin’s Will is very long and complicated. [Her Uncle}, Anthony [Thomas] Devis, originally purchased the Albury House. Ellin Devis acquired Albury by granting him [Anthony Thomas Devis] an annuity of £200 a year. She [Ellin Devis] leaves Albury House to her friend Martha Morrison, on the understanding that she lets [her niece’s husband] Martin Tupper and his wife [the niece] Ellin Devis Tupper (nee Marris) occupy six rooms of the house and on Martha’s decease, Albury House is to be left to Ellin and Martin Tupper. It seems Ellin Devis was also in possession of a number of her father’s, uncle’s, brother’s paintings, of which ended up in Martin Tupper’s possession, which in turn he donated to the Harris Museum in Preston. Ellin Devis ran a school for young ladies in London, was also an author of grammar and geography books.

Brian of nzolivers.com found the autobiography written by Martin Farquhar Tupper, “My Life as an Author” mentions:
http://www.gutenberg.org/ebooks/17558?msg=welcome_stranger

1. Ellin DEVIS’ niece, Ellin Devis TUPPER (nee MARRIS), was made the heiress as adopted child.

2. Anthony Thomas Devis originally bought Albury House in 1780 [where he retired]

3. Ellin DEVIS is “of Devonshire Place and Albury”