One could understand very well her unwillingness to be a burden, etc.

etc.
Thereupon, to his profound disappointment, Mrs Verloc's mother wept some more with an augmented vehemence.
The tears of that large female in a dark, dusty wig, and ancient silk dress festooned with dingy white cotton lace, were the tears of genuine distress.

She had wept because she was heroic and unscrupulous and full of love for both her children.

Girls frequently get sacrificed to the welfare of the boys.

In this case she was sacrificing Winnie.