Funny little idea that keeps floating around in my head, probably sucks story wise but it won't leave me alone.
Au where Mara is introduced around early season three-ish of rebels and acts as sort off reoccurring antagonist, with dynamic similar to Kenobi and Ventress. They get into duels over the course of time and she doesn't make any progress to leaving the Empire/joining the rebellion (not really her story here). She isn't present for the battle of Lothal or the purgilling, idk what she's doing but she ain't on Lothal.
Rest of the war happens after that and whole bunch of other things but meeting Luke and and getting married happen sooner than in the books, and it all happens just in time for Ezra to get back and meet Luke and find out that the Grandmaster of the new jedi order is married to his 2nd archnemesis.