prolapse in hen

My Doris seems to have a prolapse. This morning she looked like she had a soft egg hanging from her behind. Later it had gone and it looked ok - feathers weat and white but then she poo-ed and there was a red protrudence. It did go back but obviously I am concerned.
She's a mad free ranging Sussex so I will not be able to catch her without worrying her. So I thought I would wait until this eve when she is roosting.
What am I supposed to do if she still has a prolapse? I dont want to make it worse.
Advice please.

Thanks

Michelle

 Hi we recently had this happen to our very friendly hen who always had something to say to you. I found a blooming egg in the nest box and as you described a thing hanging from her behind, i took her to the vet and it was the worst kind of prolapse her ovary and other bits had come out ,he said he could have stitched it in but would come out the next time she layed so we decided that was enough as the others would start pecking at it and we sadly left her with him, hope your hen is well and was only a little prolapse
                reguards  julie