This may not be at all relevant, but the imagery of the poem 'A thought from Propertius' by the 20th century poet W B Yeats relates to Cynthia and Helen. So, commentaries on Yeats may have references to research on the image of Helen in Propertius.
I tried a quick on-line search for recent discussion of Helen in Propertius's imagery. There seems little. Try F. Cairns, Sextus Propertius,The Augustan Elegist - but only on p 401:
There's also discussion, but again only on pp 15-16, in a Stanford PhD thesis by M. Y. Myers, 2008. You'll be able to find the thesis itself from Stanford, but here are details:
L'Année Philologique is our best source of information on topics like this. A quick search retrieves among others these three (apparently) relevant items:
La figura di Elena di Troia nei poeti latini da Lucrezio a Ovidio. By: Carbonero, Orestes. IN: Orpheus : rivista di umanità classica e cristiana. 1989 v. X:378-391
Les héroïnes mythologiques dans l'imaginaire de Properce
Juan José Saer´s novel La pesquisa (Buenos Aires: Seix Barral, 1994) presents a dialogue between three persons on a text named "En las tiendas griegas" (At Greek tents). This novel inside the novel shows an Older soldier talking with a Younger soldier the day before the fall of Troy. They ask if the figure of Helen over the wall is real or not. The narration run in parallel to an investigation about a crime in Paris.
Some works on this text: http://web.uchile.cl/publicaciones/cyber/13/tx24.html
Bettini's The Myth of Helen ? But I must say I have not read it by now. There is a list of names, but no index locorum which could show the author used Propertius. Might be nevertheless interesting...