I know what you mean, but I’m not sure I can differentiate Alayne from Sansa, to be honest :) I know that Alayne is, to some extent, an identity which is created by Sansa, by I still think it’s not at separate from her as she herself would like to think.
For instance, this quote, in which she compares Sansa and Alayne:
But that seemed more something Sansa would have done, that frightened girl. Alayne was an older woman, and bastard brave. (AFfC)
In her own mind, Sansa was always afraid, while Alayne is brave. I think that’s really Sansa projecting a little, maybe tired of being powerless and afraid during her whole time in King’s Landing. Imho, she’s been sheltering in this persona, in this bastard girl that she created. And this is another instance of it. Is Sansa who’s braver, I would say, and older (in more than one sense), but she stills needs to think that Alayne is the brave one. She hungers for some strenght, so she gives this ~new identitity~ courage as one it’s traits. She’s identfying Sansa with the terrible times at KL. Being Alayne has given her some agency, she’s the mistress of the Eyrie, she gives order and runs the castle. Funnily enoug, she has much more power as a bastard than as a lady. But I would interpret this quote as Sansa realizing she has changed to some extent, that she’s braver and more confident, but only being Alayne.
Sansa Stark went up the mountain, but Alayne Stone is coming down. (AFfC)
So I would say Alayne is not really that different from Sansa, that she doesn’t have a different personality apart from Sansa’s. Only that she’s a more mature, more confident, stronger version. Something she needs for the moment. Hopefully, she’ll find soon that strength on her own self soon enough :)
That’s just my (silly) opinion, tho! That’s just the way I think about Alayne, as a shield or a mark, but not really a different person with a different set of characteristics.