Older hen proplased vent + egg bound- need advise

My 6 year old mix breed hen was found last Wed. 2/5/14 with a very poopy butt and it was 10 degrees out, so I brought her in to clean her up. I noticed her vent was popped out and black (frostbite?) So I got the dog crate out and put her in a warm place for the night. Next day, I soaked her runp in warm water, applied jojoba oil inside her vent and around the vent. Nothing. Next day, I did the same thing. Tried olive oil, in and around vent and tried to feed her some too. Black wound looking a little better. She is not eating or drinking much at all. I feed them normal layer feed, flock of about 7 now. Supplement with calcium and/or crushed sterilzed egg shells. They get organic lettuce or spinach daily.
They have a nice and dry coop with access to a covered play yard and water every day.
She has never had any health issues before, but one of the hens does lay the soft shelled eggs pretty often. I'm afraid I may have found the hen.
She is straining, straining. Bless her heart, nothing is happening. She won't eat. If I "force" her by placing food in her mouth she spits it out, so I don't push the issue.
Any advise on what to expect?
Her vet appointment is tomorrow, 2/12/14 and we're thinking about euthanizing b/c of her age and she's just not showing any improvement and isn't really eating anything.
Thank you for your input.