Who can blame Anne for being sad at Kellynch, where she is considered a nobody by almost everyone?! What a demoralizing situation to be in!

How much different her attitude must be once transplanted to a setting where she is respected, and considered necessary and useful, even if inappropriately! Mary "requires" her. She is useful when her nephew is injured. Even at the Musgroves, she is useful as a pianist and a sounding board for their complaints about Mary. She is trusted and valued.

I don't care how 'rational' a being you are, this makes a difference in your self-image. I think if you were sitting in a room with Anne, you would find her more interesting and attractive at the Musgroves than at home. I think this self-confidence is something FW would notice (even if subconsciously). He might also note how the others respect her. It is a different view than he would have had at Kellynch back in '06.