the mc divorce her husband then marry her husband's dad. I'm not sure of the genre sorry. ty in advances.
https://www.novelupdates.com/series/i-became-the-stepmother-of-my-ex-husband/ One of the few novels I've bothered to MTL. Although MC dies here and goes back to past, instead of a divorce so maybe this was not it? https://www.novelupdates.com/series/married-to-the-male-leads-father/ ? https://www.novelupdates.com/series/rather-than-the-son-ill-take-the-father/ ?
i became the stepmother to my ex husband does not include going back to the past tho. u must be mistaken. the MC original body died true, but she reincarnated as another person and she realised that it was like, a year after her original body’s death