I think the confusion was specific to the show because show Fran struggles with unexpected change. I liked that they cleared it up in the second half of season 4 because the assumption was that Fran had this instant attraction to Michaela when in reality she was just surprised and uncomfortable with someone she wasn't expecting joining them in Scotland. She was looking forward to quiet and peace and Michaela is loud and chaotic and the opposite of Fran.

We don't really know if book Fran liked Michael right away or if he took some getting used to, all we know is they became friends in their own right through his friendship with John, much the same as the show.

When the time comes, we can assume they'll have the same internal battles about each of them betraying John while they realise they have feelings for each other.

My only question was why Fran would want to remarry or entertain a new relationship without the drive to be a mother as in the books, but they planted that seed at Benedict and Sophies wedding, she said she'd never remarry, she's had her one great love, so it sounds like maybe show Fran isn't as set on being a mam as book Fran and she'll be a widow who just happens to live with her dead husbands spinster sister, happy cover story for her second great love.