Found it!

Ainsi malheureuse suis/So unhappy I am// Je ne verrai jamais nuit/I'll never see another night// Que seulement celle d'anuit/Than tonight,// Ni jour que celui de demain/Nor a day, other than tomorrow.

Ainsi m'occirai de ma main/ des trois cent dix chevaliers/ dont ce chastel était garni/ n'est céans resté que cinquante.//

À un chevalier moult maux/ Anguinueron le Sénéchal/ Clamadieu des Illes, menés/ mis à mort ou emprisonnés.//

De ceux qui sont en prison mis/ m'est-il autant comme des occis,/ que je sais bien qu'ils y mourront,/ demain, si Damedieu ne fait.//

Lui sera ce chastel rendu/ qui ne peut être défendu/ et moi avec comme captive,/ et moi avec comme captive.

There was a better translation than mine in the liner notes ; also one into more normal French. If anyone likes, I'll post them. Generally, it's about how distraught she is that almost all her knights have been defeated by the evil knight, and that she will be taken prisoner tomorrow. It's from an adaptation of "Le Conte du Graal" -- Chrétien de Troyes. I rather doubt that you could find it online, but it may be out there somewhere. In any case, it's definitely not related to the original text (well, perhaps you could say that she's also "reflecting the emotional struggle of war" -- but in this case, she's only struggling because she's losing!)

Tell me if you'd like English or modern French (and I've got the liner notes, so it will be a better English version than mine above!).

Aoede