Completed Dress and Textiles, London: Artists and Subjects, Portraits: British 19th C 11 Can anyone confirm the sitter's identity for this Lord Leighton portrait?

It must be correct that the sitter is Lena Dene (born Isabell Helena Pullen in 1873), youngest sister of Leighton’s most famous model, Dorothy. The only reason this has not gone noted in the extensive literature on Leighton is that the painting is so little known. Also, because the other images of her tend to be in private collections, the comparisons have not been made.
Considered unlocated by the Ormonds in 1975, Yasmeenah has not appeared in any of the recent exhibitions in which Leighton's art featured. So it is a good one for the PCF to have highlighted.
Comparisons with other known depictions of Lena confirm the identification: Kittens (RA 1883) http://www.christies.com/lotfinder/lot/frederic-lord-leighton-of-stretton-pra-kittens-963204-details.aspx?intObjectID=963204 and Letty (RA 1884) http://www.leicestergalleries.com/19th-20th-century-paintings/d/neo-classical/frederic-lord-leighton/13294
She looks older in Gulnihal (RA 1886) http://www.wikiart.org/en/frederic-leighton/gulnihal-1886.
Yasmeenah shows her with short hair and must date from the early 1880s.
As a child, Lena had a distinctive softly curled fringe. Her delicate features appealed to the Leighton and she should be counted as one of a small group of individuals who inspired his art.
As Barrington and others noted, not only did Dorothy Dene receive money from Leighton’s will but so did her sisters, indicating his commitment to them. Lena also had a career in theatre and lived well into the 20th century, far longer than her sister Dorothy who died only a few years after Leighton.

That's excellent news, many thanks indeed for the confirmation.

I have had confirmation from Daniel Robbins, the curator at Leighton House Museum, that the information and conclusions above are all quite correct. This is certainly a very beautiful painting and it is good that the PCF has highlighted it. This discussion can now be satisfactorily closed.

Would the collection like me to amend the title?

We should be careful to distinguish between the title of a painting and the identity of the subject. As is clear from Barbara Bryant's comments, Leighton exhibited portraits of Lena under different titles. Acting essentially as a model, she is portrayed here in orientalist dress holding peacock feathers and given an Arabic name meaning "sweet-smelling flower" I believe. This is part of Leighton's interest in orientalist subjects. The title given by the artist should be retaained as the title of the painting. The identity of the sitter or model is a separate though valuable piece of information.

Agree with Andrew - the picture was exhibited as 'Yasmeenah' in 1887 (owned by The Fine Art Society who apparently also published a photogravure of the work) and is listed with the same title in Edgcumbe Staley's 'Lord Leighton of Stretton'.

Completely right, Andrew, and an important distinction to make. Lena was the model. It's not really a portrait. The painting is what in 18th century/early 19th century parlance would be called a "fancy picture". Leighton probably considered it a potboiler, although it is a rather lovely one.

McLean Museum and Art Gallery – Inverclyde Council are you happy for me to close this discussion without changing any core data?

McLean Museum and Art Gallery has replied through email as they cannot access the site:

"I am happy to leave the ‘Yasmeenah’ details as they stand and close off the discussion – the identity of the sitter is really a secondary issue thought I was delighted to get the confirmation."

The following description has been agreed with the collection:
"The sitter is Lena Dene (born Isabell Helena Pullen in 1873), youngest sister of Leighton’s most famous model, Dorothy."