Mrs. Delacroix is one of those villagers who blindly follows tradition; in others words, as Ralph Waldo Emerson wrote in his essay "Education," she is dulled by "the opium of custom" that Old Man Warner demonstrates as he says,
"Used to be a saying about 'Lottery in June, corn be heavy soon.' First thing you know, we'd all be eating stewed chickweed and acorns. There's always been a lottery."
So, while she prattles about Tessie Hutchinson's being on time and is friendly to her, she also impatiently urges Tessie to "be a good sport" about drawing names for the trivial reason, "All of us took the same chance."
Therefore, in Mrs. Delacroix's mind, because the lottery is a time-honored tradition, Tessie Hutchinson must accept the conditions of this ritual and follow along and "be a good sport" about it, too, and not complain about the lack of fairness to the lottery. Secretly, she is also relieved that it is not she who has been chosen, and she is sadistic enough that she picks the heaviest stone she can carry in her two hands. Moreover, this sadism provides her another reason to rationalize the purpose of the lottery.