This addition to the text seems motivated by a wish to make Margaret Saville a less
shadowy presence behind it. The implicit suggestion is that she is sufficiently older
than her brother to have cared for him when they were orphaned, though, considering
the twin facts that she has children in her own family and Robert is now 28 years
old, we must assume that the difference in age would amount to something like a decade
(III:WC:11). The added phrase also emphasizes the role of feminine nurturer assumed
by all the prominent women of the novel.