Sad Day in The Hen House .....

I usually spend a bit of time each day watching the hen house girls....just for the pleasure of watching them and also to make sure they are all ok...yesterday I noticed one of the girls was continually straining and lifting her tail and I caught a glimpse of featherless, dirty bottom which looked very odd...I prepared a salt bath and popped her in it and then noticed the area below her cloaca was very red and swollen...it appears to be full of fluid and she is waddling....I have no idea what this could be and Google has put up a few suggestions.....I isolated her into a smaller cage and brought her inside and have kept my eye on her overnight...while she appears bright enough and is eating and drinking.... her poop is very strange in colour...some of it looks like cooked egg... and her bottom is getting more swollen...I have made the decision to take her to the vet and put to sleep...she is almost 3 years old and I'm not going to put her through things suggested on Google such as piercing the swelling with a syringe and draining fluid or putting anything into her vent....I've put her in the sun....she's had yoghurt (her favourite) and water and now off to the vet...I only wish I had it in me to put her down myself but I am not brave enough....it's a sad day and more tears will be shed before the day is over

She looks really well from the front end...a little trouble standing straight..

Her rear end tells a different story...it is almost touching the ground when she stands

The swelling is causing her feathers to stand out...it is warm to touch and swells below her legs

I would be interested to hear if anyone else has had this problem with their hen.....it's not vent gleet, could be Ascites found here ..she may be laying internally....the prognosis is not good and she could possibly live for a little while getting progressively worse.....but I don't want her to suffer unnecessarily . It's  a hard decision... this website helped enormously , but I think it is the best solution for her.