Poorly hen - it's Saturday, the vet is shut...

Can anyone give me advice about my poor little hen, Jenny. She has been laying soft shelled eggs on and off for a while - I've upped the calcium and bought some ex battery layer pellets and she seemed to be doing ok. However, on Friday morning her feathers were streaky with what looked like diahorrea but could have been broken egg. I washed her feathers and noticed a line of what looked like soft egg shell coming from her vent. I tried to remove it but she became quite upset, so I left it.
Today she's very thirsty and not herself at all, she's still got dirty feathers round her vent area and her appetite is poor. The others are being a bit bossy with her.
What should I do?
Any suggestions?

Thanks for your advice nnbreeder, she was much the same today but wobbly and I called the emergency vet for advice - it looks like she has a broken egg inside and there's not much that can be done.
Very hard, she is my favourite hen. They are very fragile creatures really, it doesn't take much to upset them.

brilliant information nn

Thanks for the advice and information - this little hen is not insured and I really couldn't afford a major surgery for her.
However, I decided just to make her as comfortable as possible. I gave her a warm bath and the quarter tums that nn suggested and she seems to have picked up a little. She's still drinking a lot - and sometimes the water runs back out of her beak, which is worrying -  but she's started pecking a little at food too.
I'm going to keep my finger's crossed and hope that she'll turn out like your hen, nicchick, and defy the vet's prognosis.