Eberhard:
There you will find the statement:
Diese kleinen Andachtsbildchen, die von Funktion und Ikonographie her gesehen, die unmittelbaren Vorläufer des Mediums Einblattholzschnitt waren, wurden in Klöstern, meist von Nonnen, angefertigt.
In english: [one of the predecessors of single-sheet wood engravings] had been small devotional pictures which were produced in monasteries, mainly by nuns.
****** If there is any document, that indicates that nuns were active in producing devotional pictures, it's okay.
This doesn't give any hint, how playing cards were produced, so the statement: "playing cards were mainly painted by women", as far it is not backed up with something (and as far I know, there is nothing, and if there is something, I wish to know about it), is totally unreliable - a mere conclusion. And perhaps a bad conclusion, cause any person, who is really mentioned in the production processes of playing cards in documents, is male. As there is probably no female art in 15th century, perhaps some exceptions, this was probably a male domain. Probably women were even not allowed to become acquainted with the material nor they had a chance to enter a guild.
Some nuns painted ... this might be true, as nuns often had a rich background, when they descended of a rich family. But they're unlikely to have painted playing cards.
So I guess, the author did a wrong conclusion, and stated it as truth in his wish to tell his story, as it often happens. I guess, he cannot back it up with a document - and if he could, then it would be interesting to know his source.
I don't exclude, that in the backrooms women really helped in the production of playing cards, but .... the shop owners probably were men.
There is an interesting approach of a young intellectual woman, who discussed with Guarino in Ferrara to be allowed to study something, but was disappointed in her interests. Ferrara was probably "most modern" in the relationship men-women ... and became reknown for its most emancipated and cultivated Este-daughters later.
But early playing card history is before-Ferrara - the statement looks unsolide.