Final answer:
To encourage the student to return next week to buy the dress, tell her about the sale and offer her a discount on the dress.
Step-by-step explanation:
To encourage the student to return next week to buy the dress, you should tell her about the sale and offer her a discount on the dress. By informing her about the sale, she will be aware of the opportunity to purchase the dress at a lower price. Additionally, offering her a discount will make the purchase more appealing and increase the likelihood of her returning.