Has anyone considered that the marriage is a way to redeem the White Court? Mab has a long-term plan for them, and the marriage is part of it.
We need to know more about the origin of the White Court, it must tie into the predecessor beings of the Queens of Faerie.
Besides Lara has to comply with this old charm on her wedding day, and wear:-
Something old,
Something new,
Something borrowed,
Something blue.
There is likely plenty old she can wear, Etruscan? Something new jewellery of some kind as a gift. Something borrowed, most likely from Mab, (and that is going to bite her) something blue? Carlos Testicles?
I don't know about redeeming the entire White Court. However, the last time I reread White Night; specifically Harry's final conversation with Lash, and even more specifically, when Harry had an epiphany that the Black Court of vampires has a connection with the Outsiders, instead of wondering what that connection might be, I started thinking about the other vampire courts.
The Red King was the progenitor of the Red Court, but what created him? Seeing as the Red Court is most likely totally dead and gone we may never find out or perhaps it will get mentioned in passing. More important and I think more interesting is the creation of the White Court. Uriel told Harry at the end of Ghost Story that the road of a White Court vampire was a difficult one. Something about being mortal but having the difficulties of immortality. Lately, I have been thinking that Uriel was hinting at something. Perhaps the creation of the White Court wasn't a cosmic accident. Perhaps they were created with a purpose in mind. A purpose so important that it was worth gifting them with the monstrous tendencies their demon gives them. I think they were meant to keep the other vampire courts in check, back when mortals had only a very limited ability to do this themselves. So it might be possible that Lara could be redeemed, though I'm not betting on that happening.
There is one other factor that could possibly change Lara Raith or any White Court vampire, though not necessarily for the better. What I'm thinking about could go either way. Harry has a proven ability to change the nature of some supernatural creatures by giving them names, or more accurately, by renaming them. So far, Harry has referred to Lara as Pheromone Lass in one book and as an apex sexual predator in Peace Talks. Neither of these names has stuck as a nickname. It seems that Harry will be spending a lot more time with Lara, which increases the chance he will come up with a nickname for her. If Lara starts to respond to that name you will know it is having an effect.