They should not do it if she could help it.

Never! Mary Vernon had been a high-spirited girl, and, although those who had only known her through her widowhood would have taken her for a gentle and quiet woman, whose thoughts were entirely wrapped up in her boy, the old spirit was alive yet, as with head thrown back, and an angry flush on her cheeks, she declared to herself that she would defend Ralph's rights to the last.
How or in what manner she did not ask; she only knew that those who would defraud him were her old enemies.
Had it been otherwise the fact that they were Herbert's sisters would have softened her toward them; now that fact only added to the hostility she bore them.

They, his nearest relations of blood, had ruined his life; now they would defeat his dying wishes.

It should not be if she could help it.

She would fight against it to the last day of her life.