Not sure if this is helpful since I can’t really answer most of your questions, but my bun does sneeze some as well and I’ve noticed it after he grooms. In his case though he also has a bit of a runny eye, but my vet also wasn’t overly concerned about it since he is otherwise behaving normally. She thought it could possibly be allergies or the fact that his immune system was still developing (he was about 5 months at the time the vet said this, he’s 6 months now).
Is the sneezing new with your bun or has it been present since you got her? I’m my case he has been sneezing since we brought him home (10 weeks old) but never with any discharge and usually only once or twice in a row, so I wonder if maybe he’s just a sneezer. He does seem to sneeze less now than he used to though. Hope this helps a little and that someone else can answer more of your questions

A sneeze or two a day is not very indicative of a URI in my opinion. The likelihood, with that frequency, of it being a nasal irritant like hay, fur, dust, etc. is much more likely; however, if you find the sneezes are getting worse over time, then this is more URI-like.

Sneezing is a bodily mechanism to help clear the nasal cavities, so letting your rabbit sneeze it out is not a bad solution in general — things are going to get up there, and if your rabbit doesn’t seem to be doing more than 3 sneezes a day, that’s a positive sign.

To rid of allergens, dusting and vacuuming helps, as well as an air filter. For fur irritation, generally grooming the face would be good! Hay dust can also cause it, or litter dust, so shaking that out/minimizing that may help.

It’s great that you’re being so observant of your rabbit’s behaviors, especially those health-related items, like eating, drinking, and pooping.

Any colored discharge will generally warrant a vet visit. Clear is normal, but any color such as white, yellow, green are signs of an infection of some sort.

In terms of frequency…. I can’t really give you a cut-off. My Wick would have a sneeze attack (10-12 sneezes in a row) every 15 minutes continuously, so that was definitely an extremely high frequency.

I’d say think about when you’d consider you’re sick when you start sneezing. What’s the frequency like, and things of that nature.

Sorry I never got back to you! Like human sneezes, I feel like you can hear the gross snot move for rabbit runny nose sneezes as well. But it’s such a short noise, so sometimes it’s hard to tell!

If the dryer sheet carries a strong odor, it may be a nasal irritant and help!