Final answer:
Lydia has been invited to various locations, including Brundisium with Marcus Laenius Flaccus, the Paris opera (potentially with an observing gentleman), and the Chateau de Chillon with Mr. Frederick Winterbourne.
Step-by-step explanation:
The various excerpts mention Lydia in different contexts, indicating she has been invited to visit multiple places with different companions. Lydia has been invited to Brundisium to stay at the house of Marcus Laenius Flaccus. Lydia, who is Cassatt's sister, is depicted at the Paris opera, where she is observed by a gentleman across the room. Another Lydia seems to be prepared for a visit to the Chateau de Chillon with Mr. Frederick Winterbourne, as mentioned by Mrs. Costello in reluctance. However, it is crucial to understand the context and background of these excerpts to pinpoint exactly where and with whom Lydia has been invited to visit.