The text actually states that Nabokov's mother hated "broken illusions." This is something that is demonstrated with an early memory that Nabokov has of when his mother was laid up in bed expecting her fourth child and she makes Nabokov and his brother promise to not open their Christmas stockings themselves but to bring them to her bed so that she can see them open them and enjoy their surprise and joy. Of course, what Nabokov and his brother do instead is to open the presents themselves in their room as they cannot wait to see what they have received. They then wrapped them up once more and enacted the kind of show they thought their mother would like:
...we had so messed up our wrappings, so amateurish were our renderings of enthusiastic surprise (I can see my brother casting his eyes upward and exclaiming, in imitation of our new French governess, "Ah, que c'est beau!), that, after observing us for a moment, our audience burst into tears.
This does not make her a materialist in any sense, however, as later on, during the First World War, she served as a nurse, and worked with "crippled peasants." Rather, it is her hatred of broken illusions that makes her so sensitive to the pain and misery around her, whether that be in war time or in the course of normal everyday life. Thus, although Nabokov's mother does dislike broken illusions, it would be wrong to assume that this would make her a materialist.