I am not a et, but it does sound like the hay dust is the culprit since she only sneezes when she’s digging in her hay. No discharge or physical ailments accompanying the sneezing, so it doesn’t sound like an emergency.
The only thing that is just slightly concerning is the number of times your bunny sneezes. Once or twice isn’t a big deal, but when I tell my vet about sneezing (when I had a bunny who sneezed more), she would always ask me if it was just a couple of times or a few times in a row, and if it was a few times in a row, then that could be cause for concern. So, if there is a nasal or tooth issue that is just made worse by the dust then that would be cause for concern, but at this point I don’t see it as an emergency unless it is accompanied by other physical symptoms.
Start shaking out the hay and see if that helps. If it doesn’t, then make an appointment with a rabbit savvy vet to make sure there isn’t some other underlying issue that is just made worse by hay dust or some irritant.