What may have influenced Lavinia to notify Miss Minchin about the banquet the earlier day?

Jessie and Lavinia argue about Lavinia's choice to report on Sara: Lavinia defends herself, while Jessie expresses horror over Sara's working conditions. Sara, though, looks healthy and happy after her surprise, much to Miss Minchin's chagrin. Sara is treated even more cruelly than usual, but when she returns to her room, it has been utterly transformed again, even more extravagantly. Every evening, when Sara returns to her room, she finds new additions. One day she finds a package addressed to "the girl in the right-hand attic," and opens it in front of Miss Minchin. It contains practical, expensively made clothes and a note promising that more will be provided whenever they are needed.