
'Thoughts at Sunrise' by Nita Moncrieff dates from 1880/1881: it is dated by the signature.

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress
This is catalogued in MacDonald 1995 (cat. rais.) [more] (cat. no. 833).

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress
A tree branch in the foreground, the silhouette of a city on the horizon.

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress
According to the Pennells:
'Mrs. Lynedoch Moncrieff was composing the music for some verses of Owen Meredith's. Whistler said he would like to illustrate them. She told him they were about the lark. "Charming," Whistler said "but dear me, what can I do when the only larks I know anything about are larks on toast." She bought from him a small marine.' 1
Edward Robert Bulwer Lytton ('Owen Meredith') (1831-1891) wrote a love poem, 'Thoughts at Sunrise',
'The lark leaves the earth, /With the dew on his breast,/ And my love’s at the birth,/ And my life’s at the best, /What bliss shall I bid the beam bring thee/ To-day, love? / What care shall I bid the breeze fling thee/ Away, love? / What song shall I bid the bird sing thee,/ O say, love? / For the beam, and the breeze, And the birds—all of these/ (Because thou hast loved me) my bidding obey, love. / Now the lark’s in the light,/ And the dew on the bough,/ And my heart’s at the height/ Of the day that dawn’s now.' 2
But it is not clear that Whistler is actually illustrating this.

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress
The distant view, though imaginary, looks like Venice.

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress
It is known only from the photograph in the E. R. and J. Pennell Collection, Library of Congress.

'Thoughts at Sunrise' by Nita Moncrieff, photograph, Library of Congress
See also an almost identical drawing, 'Thoughts at Sunrise' by Nita Moncrieff m0834.
It is difficult to establish Mrs Moncrieff's identity. According to the Pennells, Mrs Moncrieff bought 'a small marine' from Whistler, but this has not been identified or included in this catalogue. 3
Marriage records for Adams County, Mississippi, list 'Clarence Mackey' and 'Mered Cayetano' as married on 5 February 1844. New Orleans births in 1845 include 'Antoinette Therese Mackay', daughter of 'Clarence Wade McKay' and 'Merce Caitano'. Caitano and Cayetano could be misspellings of Caetano or Gaetano, and Mackay and Mackey, variants of Mackie.
On 10 December 1878 'Antoinette Gaetano Mackie' married a retired Commander in the Royal Navy, Lynedoch Needham Moncrieff (1841-1883). Her father was recorded at that time as John Clarence Mackie of New Orleans. The Moncrieffs lived near Whistler, at 75 Cadogan Place in Chelsea. They had one daughter, Mary Mercedes Julie Moncrieff (1880-1974) who married Henry Crofton Schneider (1876-1939).
The 1901 UK census records 'Antoinette Moncrief', aged 49 (that is, born ca 1852), widow, born in Havana, Cuba! The 1911 UK census lists Mrs Lynedoch Moncrieff, widow, 'Artist composer', aged 56, and thus born ca 1855, in New Orleans, her nationality being given as 'Spanish/Scotch', and this ties in with her birth-place as recorded in 1845, but minimised her age.
Death and probate records list the death of 'Antoinette Marie Lynedoch Moncrieff' in Kensington on 25 July 1937.
1: Pennell 1921C [more], p. 227.
2: Poems of Owen Meredith (Honble. Robert Lytton), Tauchnitz, 1869, pp. 30-33.
3: Pennell 1921C [more], p. 227.