Is she acting sick?
I see a mention of having a poopy butt, but that's the only symptom I read, I may have missed something.
I'd clean her up really well, blow dry her if it's cold where you are and put her with her flock.
Check to make sure her crop is emptying overnight and while you have her gathered up, do a check for lice/mite.
See that she's eating a nutritionally balanced poultry feed, has oyster shell free choice and grit (crushed granite) available.
Plain fresh drinking water.
Some hens are messy than others, if she's acting fine, isn't having any issues laying eggs, is eating/drinking, active, then I'd monitor her. Getting a fecal float through your vet is always a good idea, this can give you information as to whether she needs deworming or not.
Sorry, can't believe I didn't mention her behavior! Yes, she is acting sick. She's straining & having a hard time pooping. She'll get fluffy, pull her head in & close her eyes- you can tell she's pushing. She is eating/drinking.
I will check her crop in the morning to make sure it's emptied. It seemed empty this morning but I'm not sure: if it's empty, should I feel absolutely nothing? or would I still feel a slight little something something that's the crop itself?
Her regular diet is Kalmbach Organic Henhouse Reserve, mixed with red pepper flakes. Of course, mealworms too.They do have oyster shell & grit free choice & I poop scoop the coop daily, & currently deep litter method for the run until spring.
I also failed to mention that I have 4 other hens who are showing no sign of any ailment. 3 of them are New Hampshire Reds, also almost 3 yrs old & the other one is an olive egger who is almost 1 year old.
My Green girl did have a sister Rhode Island Red who had water belly. We discovered it in May, drained her a handful of times but she ultimately passed in August (& took a piece of my heart with her). Mentioning this just in case it's important genetically...?
I am on the east coast & we just got a foot of snow. Since we never really get snow, we are all shut down. No chance of a fecal float until at least Monday (at the soonest?). I brought her inside on Sunday, when it was about 65 degrees. Now with a foot+ of snow, I wasn't planning on putting her back out anytime soon. Not until it warms up, or I might be able to acclimate her to the cold again in the garage.. I suppose I'll cross that bridge when I get to it.
Thank you so much for your reply!