We don't really know what the plan was so far as Angelique vs. Laura goes. In the SHADOWS IN THE '90s: The Dark Shadows Concordance 1991's section for Season Two it's stated that:
The writing staff was quite interested in developing Roger's character - the romance with Maggie and the mystery about his wife were elements they intended to explore further. Laura Collins would have been an integral part of the storyline. They discussed many different options. It was suggested that Laura would actually have been Angelique all along, but it is doubtful they would have followed that particular avenue. Laura would definitely be identified somehow with Angelique - and it was intended that Lysette Anthony play the role - without actually being Angelique. She could, perhaps, have been possessed by Angelique prior to her institutionalization. Or she could be a phoenix with supernatural powers of her own, as she was in the original series. The 'catfight' of all time was envisioned - a battle of the witches. There would also be a nod to the Gene Tierney movie "Laura".
They did intend to bring Angelique physically into the 20th century, to incarnate her somehow.
The sad thing is that Campiti & Co. had conferred with the writers to pin things down more concretely so, among other things, Innovation's Book 3 of the comics was supposed to flesh out more about Laura, but the company went under with only Issue 1 being released. I haven't read that particular issue in years, but as I recall they only got to touch on Laura very briefly in it...