DON'T go cold turkey!!!! It's way too hard on your body and on your lo. Have you tried pumping to add some EBM to the soy milk? As you're doing this, you can gradually drop feeds during the day and just offer the sippy cup (what kind are you using?). She'll get the hang of it - once she figures out that for that feed, she just gets the cup and not the breast... If you want to stop offering your breast too, you can always pump a feed for a while and give her the EBM. Then start pumping less and less for that feed and replace the extra with the formula. Until finally, you're not pumping for that feed at all. Then work on another feed during the day.