Actually, it can be insinuate that she had been using her luck for a while, as she had used it on Marsh earlier, and she was pretty good with it at the beginning of Mistborn 1 so we can kinda assume she had been using it for a while, and i always assumed he had been gone a few months, definitely less than a year. Do we have a WOB on how long before the beginning of Mistborn 1 Reen left Vin?