Painter p.348: "On 9 September he tried to persuade Antoine Bibesco to write a publicty-notice in Gil Blas for Louisa de Mornand [...] But Antoine failed to be moved by this testimonial, and Proust was forced to write the notice himself, and another early in December."
Letter to Antoine Bibesco [9 September 1904]: "As for the snapshot, Louisa has taken seriously what you probably just said off the top of your head. So you ought to do it. But in any case if you prefer me to do it I won't sign it for anything in the world because it will have to be done as inanely as possible, like a sort of pastiche of Delilia: 'Remember this name, it might well break through one day!' - or 'She is a zealot for her art, a grafter'. I'm sure you would do that wonderfully." Corr. t.IV, p.243
Letter to Louisa de Mornand [14 September 1904]: "I wrote the "cameo" Louisa de Mornand for Gil Blas. I don't know when it will appear." Corr. t.IV, p.259
Letter to Louisa de Mornand [30 November 1904] : "It looks like perhaps I am going to be able to get a few words about you passed on to Gil Blas, which I will be happy to do." Corr. t.IV, p.362.
Gil Blas, 9 November 1904: "LE THEATRE Au Vaudeville - Maman Colibri comédie en quatre actes, de MM. Henry Bataille. [...] It would be completely unjust not to praise the authority of Mlle Paule Andral, the prettiness of Mlles de Normand [sic], Welsonn and Becker."
I have been unable to find any mention of Louisa de Mornand in Gil Blas for December 1904.