(Source: fordham.edu) (LINK)
The Cain Adamnain, also known as the "Law of Innocents" is one of the earliest examples of International Humanitarian Law, providing protection for women and non-combatants in war.
Within the treatise contains are rather disturbing description of a class of slave women known as the Cumalach. In contrast to the romanticized image of Celtic women as being fierce warriors - encapsulated by figures such as Boudica - the Cumalach here are presented in a grim fashion that brings to mind a conscript, being forced to fight by her male superiors while being of lesser status and rights.
Since Adomnan lived in the 7th century, this practice could possibly have been present during the Arthurian era. Meaning King Arthur and the Knights of the Round Table would have encountered these women in their various wars and adventures, especially those involving the Irish.
I can imagine a potential narrative theme developed in relation to the concept of Celtic Warrior Women - both the good and the bad - and the (Male) Chivalric Code. The Cumalach, almost feeling like an inversion of the chivalric dynamic of "knight fighting for a lady", present an interesting dilemma for the KotRT to struggle against and even informing their personal beliefs about the Chivalric code and the treatment of women both in war and in court.
There's also another thing to consider: Arthuriana itself contains a few named female warriors/knights, the most famous being Britomart (as well as Guinevere, in modern actionized versions). The Cumalach would serve to contrast a stark reality of Celtic warrior women, separated by social class*, with one group being able to become prestigous knights while the other group are treated as disposable cannon fodder. Introspection by heroines and ladies abound.
*It should be noted that the named female knights (Silence, Britomart, Grisandoles, Melora, etc.) are from nobility, with some marrying into higher stations. Whilst the preceding Boudica herself was a queen.