My dog has sneezing fits and is scratching. What should I do?

This could be due to dust, or strong scents in the environment. I would first check to see if that's a possibility. Things like sand storms, construction, perfumes and smoke can irritate the nasal passages and cause them to sneeze like this.

An infection is also possible. Sometimes they can get a mild infection similar to a cold. These infections have the possibility to go away on their own, or can get worse with time.

The scratching is suspicious of an allergy, but could also be due to other things like fleas or mites. A vet would need to exam Margo in order to determine this.

If Margo starts having nasal discharge, loses energy, or otherwise seems worse, then I'd recommend taking her to a vet.

I hope that helps and Margo gets better soon.