@ greenhorg that's right, she really wasn't in love with him. The movie actually makes it clear with the last intertetitles, that says something like "how she lied to Mr. Emerson" just right before she "confesses" her love to George, making it clear she really wasn't in love with him. She was however in love with another man, her brother (as strange as it might sound). Take a closer look at the way she watches her brother constantly and the small hints of sexual tensions whenever she talks about him to her "supposed" lovers, Cecil and George. Take also special notice of how she reacts in the bathing scene and how differently she looks at each one of them. And like you pointed out she seems more interested in the letter from her brother than in her husband in the final scene.

Cecil Vyse was hilarious and painfully prim

No one exemplifies the primal lust and wild emotions of young love better than mannered, 19th century, upper crust England.

Honestly I don't see much evidence that Lucy was into George much more than she was into Cecil. The one "love scene" (the cover of the box) was him pawing at her while she tried to read a letter with a mildly annoyed expression.