As far as Jehan being involved in the twist:
1. Divorced isn't a big deal (Bob, Kara?, a few of Byron's Bachelorettes)
2. exMuslim I don't think is such a big deal. (Now if she were currently muslim, that would shake things up!)
3. exModel isn't a big deal. Unless she did porn. Then she would be Fleiss' dream Bachelorette, and the focus of the show (and an automatic producer pick F2).
4. Wanting to bail on the Doc. Many have done that before (to Trista during RC, to Andrew before second RC, to Jesse on a group date, to Jen during RC, to Charlie on a group date).
5. Even showing up at the RC after dumping the Bachelor has been done before.
Because of this I think the twist must be something else. But what? If it's not Jehan then who, and when?