Final answer:
Estelle says the phrase 'buenos días' to Vanessa as a way of greeting and acknowledging the start of the day.
Step-by-step explanation:
In the given passages, Estelle says the phrase 'buenos días' to Vanessa because it means 'good morning' in Spanish. This phrase is used as a greeting in Spanish-speaking countries, similar to the English phrase 'good morning.' Estelle is using this phrase to greet Vanessa and acknowledge the start of the day.