I don't think the pink thing in the westfalia was MM - why would he stay local? Keep her in the van give her lollies, meals, let her out to pee etc? It's nonsense imo. He didn't have time to groom her, there was an international search party out for her.
MM would have been killed very soon after imo.
However, after having taken MM and possibly abusing her, his fantasies, (in the chatroom) would have been even more developed, sick and enduring. - hence, talking about taking something small and using it for days.
If he knew he had done it once and had got away with it and had been sexually gratified by it, then his fantasies could go to the next level. (Fritz style)
JMO