vacuum, because of her tumble of feelings on seeing him again? In other words, read this:

CH. 7 -

" "It is over! it is over!" she (Anne) repeated to herself again, and again, in nervous gratitude. "The worst is over!"

***Mary talked, but she could not attend***. She had seen him. They had met. They had been once more in the same room."

So if she was in the room, yet didn't listen to Mary talking because of her own thoughts, which seemed to spread through the time the girls walk with the men. Then, when they return, we are still party to Anne's thoughts, when Mary breaks in with her revelation. So if it says Anne could not attend Mary's talking, could she have perhaps been so wrapped in her own thoughts that her presence was overlooked, and she had not heard the first hand account from the girls, given to Mary?

And then further on, same sequence:

"On one other question, which perhaps her utmost wisdom might not have prevented, she was soon spared all suspense; for after the Miss Musgroves had returned and finished their visit at the Cottage, she had this spontaneous information from Mary --

"Captain Wentworth is not very gallant by you, Anne, though he was so attentive to me. Henrietta asked him what he thought of you, when they went away, and he said, "You were so altered he should not have known you again." "

It says directly after this that Mary did not design the remark to give offence, she was just completely unaware of Anne's feelings, as is quite common in her family circle. So if I have this right, the conversation with the Captain takes place outside on the walk, (while they are away) and is then relayed back to Mary. Anne is not moved scene wise from the cottage, so is it possible to assume she is there, but mentally somewhere else, and doesn't hear the comment? It appears she is in a kind of shocked daze, by all that has happened? Is that what it is?