I think that the first conversation silverfish mentioned doesn't pass. Barbara is addressing both Mr. and Mrs. Darville. It's not a woman-to-woman conversation but a three-party one with a man involved.
Then at the party Anne asks Mrs. Anderson to help her taking Mrs. Cunningham upstairs. Mrs. Anderson doesn't talk bavk, though. Doesn't pass either.
There's a long plot-relevant conversation between Anne and Barbara about Bruno and the incident during the party. This one snd the Anne-Mrs. Anthony conversation make this movie a clear 2/3 pass. So, nothing wrong with the rate, IMO.
Barbara: Bonsour Madame, Monsieur, how are you?
Madame: Darville:Delighted to see you miss Barbara, how sweet you look
Barbara: I hope you aren't forgetting our little party on Thursday Madame.
I'm planning on it. (Monsieur Darville: but of course).
In any case, it definitely passes at least 2 tests, as Job says. For example, there is a conversation Anne Morton has with Mrs Anthony about Bruno (her son), and around 58 minutes Barbara discusses Bruno with Anne. I think the conversation I mention at the start of the comment is the only one that passes all three tests, and only just.