Sorry, I've not had the chance to get online recently & only just seen this.
My Sophie had a very similar thing happen a couple of years ago. Although we will never know for sure, we deduced that she had probably prickled her nose on a hedgehog.
A course of antibiotics sorted it out - after she had scared us half to death by being allergic to them as well, but that is another story!
Hope Piper is better soon.
Rachel, Sophie, Billy & Ted xxx