I've never seen anything quite like this before. The swelling, and then opening of the wound kinda brings to mind an abscess of some kind, but I can't really say, I'm no vet. I say, when in doubt, call a vet. As far as yours being out of town, try calling other vets in the area. You may get a recommendation if not a diagnosis even over the phone. Hopefully you can get someone to look at her.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown