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Guyon discreetly pulls Alaria aside and lowers his voice so they won't be overheard.
"One of the performers has stomach problems... I would be grateful if you could prepare something that is not only easy to make, as Beata said, but also dietary, so she can eat without any negative consequences."
He gives appropriate dietary recommendations based on his studies, [here is a link from Google, I'm too lazy to Google it].
He didn't point fingers to avoid violating medical confidentiality, but he revealed the gender of the performer because all the men had already eaten non-dietary food and were fine, so it's not a secret that it's one of the women.