Highlander Fallen by Rebecca Preston

Thrust back in time by a horrible accident, Karin finds herself immersed in the mystery of reincarnation and the magic of the Scottish Highlands, at the center of a deadly cholera outbreak, and caught in a growing attraction to a man grieving his lost wife.
Karin thinks things can’t get any worse than being pregnant, dumped, and in trouble at work, but a car accident sends her back in time to ancient Scotland where she awakes battered and bleeding. Her initial distrust of the dark, brooding stranger who rescues her and treats her during her miscarriage soon changes to a strained attraction as she attempts to settle into her new reality including the threat of witch hunters and a overzealous English Lord.
William MacClaren lost his beloved wife in childbirth and fled to the cover of the priesthood to hide his alchemy and to grieve her loss. When he stumbles upon Karin, the reincarnation of his true love, the pull to her is impossible to deny but the pain of potentially losing her again is too much to risk.
When an outbreak of a deadly disease forces Karina and William to work together to save lives, they must confront their growing feelings for each other and find a way to work through their past hurts.