The Third Wheel.
That's who Gwen is, the third wheel. She loves Downton and all her friends there dearly, but there is no friendship that is entirely hers. She used to have Anna, but now Mr Bates is here and things are changing. Mr Bates is a decent man, and Gwen can easily understand why Anna likes him so much – very easily. But she's being pushed out, or she's falling out, and she doesn't know what to do.
Lady Sybil trying to help her, even if it is rather a condescension, gives her hope. They can never be proper friends, but it's a start, at least. And Gwen is settling into the idea of having a friend like that. But suddenly it seems that Mr Branson is always welcomed there, too. Gwen can definitely understand why Lady Sybil might like somebody like Mr Branson – even if he is below her in a way, those eyes and that voice make it all worthwhile. And how could she compete with Lady Sybil? So she lets herself look elsewhere for friends.
She tries Daisy – the girl needs some guidance, and she's nice enough if a bit dim. But William is always following Daisy, like some kind of puppy, and Gwen can't bear to let him be pushed out like she has been. She can't see why Daisy doesn't give him much of her time, and she can't see why he gives her so much, but she likes William, and she feels sorry for him, and she...
That doesn't work, either.
So Gwen is glad to go. The secretary job takes her to London, and she keeps in touch with Anna and Lady Sybil and Daisy, but she's not a third wheel any longer. She doesn't need anybody. It's Gwen Dawson, one little wheel all on her own, and she finds that she can't think of anything better.
I wrote this about a year ago, and recently rediscovered it. Inspired by three things - augrah's Lost in the Shadows, an awesome Gwen/Bates fic; an RP featuring Gwen's massive crush on Branson; and my absolute certainty that Gwen/William was the way forward, but that the way things did go, she's doing just fab on her own.