I believe you might be dealing with a mistranslation. The version I'm looking into (link) goes as such:

"Jeanne étant tombée malade au cours du procès, les juges me mandèrent de la visiter. Le nommé d’Estivet me conduisit auprès d’elle. En présence dudit d’Estivet, de maître Guillaume Delachambre, docteur en médecine, et de plusieurs autres, je tâtai le pouls à Jeanne pour savoir la cause de son mal et lui demandai: « Qu’avez-vous? D’où vient votre peine?» Elle me dit que l’évêque de Beauvais lui avait envoyé une carpe, qu’elle en avait mangé et qu’elle se doutait que c’était la cause de son mal. Là-dessus d’Estivet l’invectiva. Il se plaignit de ses mauvais propos et l’appela « paillarde » en cette façon: « C’est toi, paillarde, qui as mangé des harengs et autres choses à toi contraires ». — « Je ne l’ai pas fait», répondit-elle; il y eut entre elle et lui un assez long échange de paroles injurieuses. Pourtant j’en voulais savoir plus sur la maladie de Jeanne. J’appris de quelques personnes présentes qu’elle avait été affligée d’un fort vomissement."

The passage recounts how Jeanne fell ill and was examined by Tiphaine, a physician, at the request of the judges after eating of fish which was presumably given to her by the Bishop of Beauvais. The reproach voiced by Tiphaine could be somewhat better translated as such, in intent: "It's your own fault, you cunt [sorry], for eating of herring and other things which do not agree with you" I do not really see that much of a link between the cussing at Jeanne and the fish eating, they should not be conflated.

I doubt the insult "paillard" was meant litterally and in the descriptive sense - the colloquial modern term "cunt" is perhaps the closest translation for "paillard".

They're not connected, as far as can be told from the source. Estivet is being insulting (which is why he calls her a whore) and then diagnosing the root of her problem (bad fish, supposedly).

This ties into a number of possible concerns for the judges of the nullification trial about the conditions Joan faced in Rouen. Was she being fed bad food? Was she given food poisoning? Did hallucinations cause her to act in a particular way? Was she simply not eating enough? The topic of Joan's food comes up a lot in the records for the nullification and heresy trial. In particular, certain witnesses in the nullification trial suggested Joan had a particularly abstemious diet: the Duke of Alencon recorded her as eating/drinking merely toast and wine after a day at Orleans, if I recall correctly. Perhaps the fish in brine (a carp, sent by Pierre Cauchon the Bishop of Beauvais and chief judge, mentioned earlier) was simply too rich for Joan. By saying what the "master of medicine" Estivet said, Tiphaine informs the judges of the nullification trial about conditions Joan faced.

As for why Joan was called a whore, that seems to be more just because Joan is a woman he doesn't like. Joan's virginity does not appear to have been seriously challenged (except in a mocking sense) with prominent figures like the Duchess of Bedford being happy to vouch for it. It's likely that he did use these words: Guillaume de La Chambre said Jean d'Estivet was abusive to Joan as well, calling her a whore and a slut (translated, obviously), in the next deposition from Paris.