Good question! I certainly started writing about her because of her marriage to Gregor, because the story I was putting together (accidentally and in increments) centered around Gregor. But the more I wrote about Laisa, the more I liked her. There isn't a whole lot about her in the books, and a lot of that is the dewy-eyed stage of the romance, but you get a sense of her practicality, and of her amused acceptance of the Barrayaran culture she's always going to remain an outsider to despite being a symbol of it. So, therefore, somewhat like Cordelia - except that her personality is more easy-going (core of steel, I think, but it doesn't show as often), her educational background is different, and she grew up within the Barrayaran Empire, if not on the planet of Barrayar itself. I think what I mostly ended up exploring was her reaction to her new status, to Gregor the man and the emperor, and to what his upbringing did to him, and there's a certain inevitability to that, because in that culture that's what an empress (especially an off-worlder one) does - she reacts, and accommodates, and fits herself in, and doesn't rock too many boats. I see Laisa as someone who thinks, a lot, before she acts (we see her courtship with Gregor as whirlwind, but really there was time in there for a good deal of contemplation), and although she must have felt a great deal of kinship with Cordelia, I suspect she absorbed more from Alys Vorpatril about how to make her presence felt and effect change. I bet she steered Gregor more strongly and quickly toward the progressive reforms he already wanted to make, but they shared a view of doing so as subtly as possible. Unlike Cordelia, Laisa must have grown up surrounded by politics - her family made a lot of money out of cooperating with the Barrayaran Empire - and understood it down to her bones. She knows exactly what she's doing, going into this marriage; she knows that she'll be a political object for the rest of her life, and that her husband always has been, and that their children will be, and she enters in willingly anyway, for love and for the benefit of the Empire. So though I think there are a lot of stories to be told about her doing her own thing separate from Gregor, in the end she's always connected to him, and accepts that, so I don't feel bad presenting her as part of his story.

By the way, I suspect LMB had all this in mind while writing, but the paucity of Laisa's actual presence in the books can lead to a view of her as just pretty and plump and turning beautiful adoring eyes on her man. So a lot of my writing her, once I got started, also had to do with, hello, a real person, with a brain and everything. And I also wanted to delve a bit deeper into the romance, which viewed from Miles's distracted POV is rather surface-level. Laisa isn't just dazzled by Gregor's sparkly palace; she falls for him as a person, and he for her. And they have troubles; it can't just be a fairy tale. And… I think she has a smidgen of sense of humor in the books, so I gave her more, but then I can't really help doing that to any character I like. But really, if she couldn't see her situation as funny, I don't think she could survive. There's a lot of fanfic that says "But it's not fair!" about how little attention certain characters get, and my Laisa fics certainly fit that bill.