Is it a big potty or a little potty? If a big one, maybe buy her a little one - My 2yo son will only poop in his Baby Bjorn potty - it's a perfect size for him.
Otherwise, consider letting her pick out one herself - or a potty seat for the big potty with the design of her choice or new undies or something special. You could let her pick one new pair of undies from the pack after each successful poop.
Once she goes a few times, it will probably start feeling more natural, but I'm sure she is in her comfort zone pooping in her diaper and pooping is a bigger deal than peeing, or it has been with both of my kids. It takes more concentration and effort than peeing - heck I still don't like to poo in public places (Yeah, TMI - I know).
I'd consider the bribes - maybe not candy, but something important to her and maybe something indicative of her being a big girl now, like the new undies or something else she's been wanting. A "special outing" is too remote for a 3yo, IMO, but if you decide where to go and talk that up, it might be ok - sit down and give her a few choices and let HER decide where to do, perhaps, to give her a feeling of control over the situation.