Final answer:
The appropriate action when a customer is ready to try on a dress is to direct them to the fitting room to provide a positive shopping experience.
Step-by-step explanation:
If a customer is ready to try on a dress, the most appropriate action to take is to direct the customer to the fitting room. Providing good customer service means assisting the customer efficiently and courteously. Being attentive and facilitating the customer's experience reflects well on the store's service standards. Based on references provided, the saleswoman assisted by slipping the dress over the girl's blouse, which signifies a high level of customer service, although typically, a customer would be directed to a private space like a fitting room to try on clothing. In a retail setting, other actions like asking the customer to wait unnecessarily, offering a different item without being prompted, or ignoring the customer would likely result in a negative shopping experience.