At first, Aoife just accepts it. Marina is trying here, and Aoife should admit to her that it is not that bad, having a sister that can't remember their shared history. It's not like it is a happy shared history, anyway.
But it is something in her sister's voice, in the pronunciation of her name that assures her that this is no pretend. Thor immediately picks up on her mixed emotions and crawls over to her, belly in the sand.

So what happens next? "Oh." She meets her sister's eyes. "Hello, Moira. Does that - do you remember everything as Marina as well?"