The relative that caused Balzac the most discomfort was the Countess Rosalie Rzewuska, nee Princess Lubomirska, wife of Count Wenceslas Rzewuski, Madame Hanska’s uncle.  She seems to have been continually hearing either that he was married, or something that was detrimental, and kept him busy denying these reports: 

“I have here your last letter in which you speak to me of Madame Rosalie and of Seraphita.  Relative to your aunt, I confess that I am ignorant by what law it is that persons so well bred can believe such calumnies.  I, a gambler!  Can your aunt neither reason, calculate nor combine anything except whist?  I, who work, even here, sixteen hours a day, how should I go to a gambling-house that takes whole nights?  It is as absurd as it is crazy. . . .  Your letter was sad; I felt it was written under the influence of your aunt. . . .  Let your aunt judge in her way of my works, of which she knows neither the whole design nor the bearing; it is her right.  I submit to all judgements. . . .  Your aunt makes me think of a poor Christian who, entering the Sistine chapel just as Michael-Angelo has drawn a nude figure, asks why the popes allow such horrors in Saint Peter’s.  She judges a work from at least the same range in literature without putting herself at a distance and awaiting its end.  She judges the artist without knowing him, and by the sayings of ninnies.  All that give me little pain for myself, but much for her, if you love her.  But that you should let yourself be influenced by such errors, that does grieve me and makes me very uneasy, for I live by my friendships only.”

In spite of this, Balzac wished to obtain the good will of “Madame Rosalie,” and sympathized with her when she lost her son.  But she had a great dislike for Paris, and after the death of M. de Hanski, she objected to her niece’s going there.  The novelist felt that she was his sworn enemy, and that she went too far in her hatred of everything implied in the word Paris[*]; yet he pardoned her for the sake of her niece.

[*] The reason why Madame Rosalie had such a horror of Paris was that
    her mother was guillotined there,—­the same day as Madame
    Elizabeth.  Madame Rosalie was only a child at that time, and was
    discovered in the home of a washerwoman.

It was Caliste Rzewuska, the daughter of this aunt, whom Balzac had in mind when he sketched Modeste Mignon.  She was married to M. Michele-Angelo Cajetani, Prince de Teano and Duc de Sermoneta, to whom Les Parents pauvres is dedicated.

Balzac seems to have had something of the same antipathy for Madame Hanska’s sister Caroline that he had for her aunt Rosalie, but since he wrote to his Predilecta many unfavorable things of a private nature about his family, she may have done the same concerning hers, so that he may not have had a fair opportunity of judging her.  He was friendly towards her at times, and she is the Madame Cherkowitch of his letters.