not eating, REALLY smelly vent, not active, nothing in crop... not sure how to treat.

My hen has been acting kinda sluggish the last 4 days. I put it off until yesterday when I noticed she hasn't been eating. She is in a dog crate and kept in our garage (its around 60s in there). She is kind of fluffed up all the time but done molting. She hasn't laid an egg in days now. I checked out her vent and her poo is a little drippy but has stopped since she stopped eating. She is still drinking. I rubbed her crop thinking maybe it could be impacted or sour but there really wasn't much in it. What I really noticed is she SMELLS! Her vent had smelled the coop as well. It wasn't noticeable until today. She is one stinky hen!
I have looked up many things but with her being somewhat sluggish it doesn't add up. Also, a couple days ago she wasn't with the other hens to free range when I let them out of the coop. She just sits in one spot and doesn't even scratch. She is the leader, so to say, and she doesn't even mess with pecking or raising her voice at me like she normally does.
I use DE for them but without her eating I don't know how to get it down her. I did put a little apple cider vinegar in her water but otherwise I don't know what else to do for her except keep an eye on her and check her crop. Any suggestions will be appreciated! Thanks!

 

Thank you all! I will start treating her for this right away. She acts pretty miserable.

 

So it has been about a week. I would like to report that she is better with treatment but she still won't eat and now her drinking has gone down. I noticed her comb shriveling up and when I washed her vent today her pubic (or pelvic whichever chickens have.) bones are protruding. She has lost so much weight. Her poo is still watery and smelly. How long should I keep treating? With no results thus far I just feel so bad for her. I don't want to lose her but I also don't want her to suffer.

 

I mean a week since her first symptoms.