alexius wrote:
The party of guests comprised Castillon of course, JB described as La Diva's manager;
I'm going to have to say that "La Diva" cannot be Emma Calve. Here's why:
In 1900 Calve was at the Met in New York and being managed by Maurice Grau exclusively. Though Wikipedia has marked the chronology for the year 1899-1900 as "Travel in Orient" it was actually pretty well documented. Let's take a look at some contemporary sources.

In
The Musical Times of 1 February, 1900 we see a discussion of Mr. Grau's capabilities as a manager, and mention of Emma Calve's illness.
The New York Times reports on 13 February, 1900 of the illness mention in TMT, and also tells us details of what Calve's travel plans are for the near future, and that she will not be singing any roles. Emma Calve left for Palm Beach, FL on 12 February for a few weeks, then will go on to Cuba. Note how she is described as a member of the Grau team:

On 21 February 1900
The New York Times gives us an update of how Ms. Calve is getting on in Florida:

These events also appear in
My Life, Emma Calve's autobiography and as we have seen are corroborated in contemporary journals. Chapter 16 (pg 135) of
My Life is called "A Cuban Interlude" and tells of her illness, her trip to Florida, and then Cuba. Then towards the end are these lines:
"...one day I received a cablegram from my manager in New York, asking me to return at once..."
That manager of course was Maurice Grau, asking his artist to come back to the city because she still had obligations to fulfill. The book continues:
"I left Havana and returned to my work."
I very very much doubt that after all this Emma Calve could be in France in May as after the Cuban interlude she went back to work (contracts being contracts after all), which puts us somewhere in March/April (? no dates found for the length of her stay in Cuba, but the book makes it sound like rather more than just a week). Either way, "La Diva's" manager is referred to as JB... not even close to MG. For someone who takes pains to write people's names in a journal as initials only, and manages to get everyone's initials right
except this one is baffling.
Then there is Paderewski...
Around this time I. Paderewski, though mainly known as a pianist, was hard at work on his opera
Manru which would premiere in Dresden in 1901. In attendance at the premiere was Maurice Grau... Grau "took notice of Paderewski's Manru before its Dresden premiere, and decided to stage it in New York after its success at Dresden's Royal Theater. More information about the New York premiere of Manru may be found in Paderewski's interviews published in the British press in mid-September 1901. He confirmed what was reported earlier, i.e. that Grau would produce Manru in New York, with the Met Orchestra conducted by Walter Damrosch..." To make a long story short, Grau and Paderewski knew each other. For anyone other than Maurice Grau to be introduced as Emma Calve's manager/impresario would be a
blatant lie sure to be noticed by people in the same social sphere.
On 12 February 1900 Paderewski gave a recital in Lincoln Nebraska, USA(
see this link) as part of an American tour sponsored by Steinway. By 9 April 1900 he had only made it as far as Boston, with still more dates to go including London:

So with a tour schedule, AND finishing touches on an opera (to not even mention the rehearsals!) again I don't see that Paderewski could have had much leisure time to spend in a castle in France.
If "La Diva" had a manager with the initials JB, then "La Diva" cannot be Emma Calve. If Paderewski was present at this party, he most certainly knew Grau, his reputation, and his connection to Calve. During the time period in question Emma Calve only had one manager, and that would be Maurice Grau. He was still her manager one year later:
