Hello and
to The Squirrel Board! Thank you for rescuing Hazel and caring enough to give her the very best diet from the start. As you indicated, diet is the number one item that we control, but often people don't know what to feed, so you have already taken care of the most important thing!
That said, squirrels do snort a lot, similar to a dog (and for the same reason). When a squirrel sneezes, often it is because they are clearing the scent receptors in their nose (just like a dog). What you should watch for is any discharge from the nose. Rex got a cold a couple years ago, and had a runny nose (along with a lot of sneezing), but we just had to let him rest and the cold passed in about 10 days.
Since I am on the West Coast, I don't have any advice for Vets in your area. I'm not even certain of the laws in Michigan and don't know if it is legal for you to have a squirrel. Please be very careful about contacting a vet until you know what the laws are in your state, as we have had people take their squirrels to the vet (or a rehab center), with the best of intentions, only to have their squirrel put down because of the laws of their state. One happened here in my state less than a month ago. I don't want to see you go down the same path with Hazel.