Alda's a pretty one-dimensional character: she loves Roland so much that when he dies, she dies too. Her big moment comes when Charlemagne offers to replace Roland with his own son, Louis, because a man's a man, right? Not for Alda. "This offer seems strange to me," she tells him with disdain, and dies immediately.
Interestingly, her request that "it not please God […] that I remain alive after Roland!" is granted (268.3718-19), but Charlemagne's similar prayer after Roncevaux, that "before I reach the main pass of Cize my soul be separated from my body," is not (210.2939-40). Does this mean that Alda, a woman, is expendable and Charlemagne is not? Sexism!