Thanks for all the helpful comments
Unfortunately, after waiting another day, she is still sneezing... although luckily the condition has not worsened.
I called a vet nearby and asked if they will treat hedgehogs and they said yes, so I think I will bring her there tomorrow. If she is stressed, what usually causes the stress? I take her out of the cage to roam around for about 30 minutes a day, is this too much or too little? The poop has turned back to brownish, but I dunno, it seems to alternate sometimes. The cat food by the way is this one: Link