It sounds like you are doing a lot of things right. You're daughter seems like she's upset by the prospect of doing her business in a new place. And it's a thoughtful question regarding the "reward system". Although my son isn't yet old enough for toilet learning, I've spent many years working with young children and this is what I've learned:
Often we are encouraged to reward our children for doing what we want them to do. Sticker charts and "incentives" are everywhere, and while they might produce short-term results, are often riddled with hidden problems.
If we consider that using the toilet is a biological function, and often not within immediate control of a young child, we have to acknowledge that offering a reward or treat for successful toilet use can potentially be confusing to a toddler.
For example, if your daughter knows that she will get a treat for using the potty, how will she feel when she doesn't get a treat? All she knows is that she didn't do something that obviously frightens her, and now she can't get something she likes. That, in my opinion, is a lot of pressure to put on a kid.
I've worked with families that have used incentives and those that haven't. The children that just went to the bathroom without a lot of fuss being made over it tended to potty train faster and seemed to have less issues around toilet learning overall. Those children that were always rewarded tended to become more focused on the prize, and less on learning their own bodies signals and responding to them, which is ultimately what we parents hope our children will do. This scenario was definitely more high-maintenence to tend to.
What happens when the child sits on the toilet and tries, but nothing comes out? Or the evidence is "undetectable"? What happens when the prizes stop and the child begins wetting again? Does that up the ante for prizes? I once worked for a family that gave their son a toy truck for every BM in the toilet. They were great parents, but sold on the "rewards" method. I'm not saying anyone else is going to do that, but it's worth thinking of these things before going down that path.
My advice: let your child proceed, without incentive, at her own pace. Wait until summer, and then, if you have a backyard, take the potty outside and let her play naked. This will give everyone a chance to relax about accidents. I'd minimize the potty talk --not make a big deal out of it-- and let her lead. Many girls don't start becoming successful at using the toilet until two and a half. Let her sit on the potty when she wants and use her diaper until she's ready to make the switch.
For what it's worth, some children are just more comfortable going in diapers. Whenever you decide to "officially" start toilet learning, I always recommend using training pants instead of pull-ups, so that children can actually feel when they are wet, and experience what happens when they wet or poo their pants. Being low-key during clean-up, and encouraging - "we'll try to get to the potty next time"- will go a long way in helping children feel competent and, eventually, confident, that they can indeed use the toilet.
I did have minute to scroll down: Kudos to the "reward" Jessica offered her children of letting them wash their hands for as long as they wanted. THAT was exciting to see, because older children tend to treat handwashing as a chore. Fun foamy soap also helps.
