OMG - what is that on your face?!?!

When I got to the barn this morning, I had all sorts of little things planned.  I was going to put the bridle on Ruby, then groom her and re-braid her mane, take squared-up conformation pics, take my time doing my chores.  Things started off well...then I noticed this.

This is the picture I sent to her vet - if you look, you can make out a swollen lump on the left side of her face (her left ya'll) near her eye.  It was hard to the touch, though there was a smaller, softer spot further towards her nose.  No nasal discharge, acting perky and eating fine.  It wasn't sensitive to touch.  The vet came out a couple hours later to check it out and gave her something for swelling.  It MAY be an abscessed tooth but judging from her lack of other symptoms (no fever, no odd smell, eating fine, lymph nodes good), it's probably just an allergic reaction to a sting from a bug.   Crossing fingers.