First and foremost, hamsters and gerbils can be very vicious, so I hope you're pre-killing them. Second, hamsters have a LOT of fur and balls can be become impacted when trying to digest it. I would stick to mice, or preferably rats. Now that you've fed her a gerbil though, she may never take rats or mice.. Can't really help you with the wasting food other than that you should stick to one food source and not try feeding it all types of prey. They imprint on a specific item and will refuse anything else, they are notoriously picky eaters.