... she was more used to having Fanny with her? Sir Thomas was the head of the household and managed matters of the estate (or was away in Antigua) while Fanny was with her aunt, reading, conversing or simply being with her. Perhaps that explains it.

I must confess I don't remember Lady Bertram displaying particular emotion when Sir Thomas went away, but when he came back she was so overcome she actually gave him a part of the sofe. And the Pug had to go! :-P