I'm sorry that Hubble is not feeling well

Thank you for the photos and further information.
With your description and photos. It does not look like she has vent gleet, there would be a foul smelling/yeasty crusty discharge on the vent and tissue underneath. Her vent looks clean.
I do think that she may have a reproductive disorder that is causing the crop to slow. Bodily functions work together just like in any other animal or human. One thing can cause symptoms some where else.
With reproductive problems, this can cause swelling inside of her that slows the digestive system and puts stress on the internal organs too. Her comb is darkening, that to me indicates organ function may be failing.
I'm very sorry. You can try antibiotic treatment to see if that helps with inflammation, but usually the results are short term. I would worry like your Mother is, that she is starving/wasting away. I would work on the crop a little more to see if I could get that moving. Coconut oil a couple of times a day with massage can help. If you think she may have an impaction, you can try 1 stool softener (stimulant free) to try to break up anything that's there. Sometimes it works, but if the crop problems are caused by inflammation elsewhere in the body, then it may not.
Keep her hydrated the best you can. If she is enjoying the cucumber then all is well, it will provide her a little liquids. You may want to offer her some watermelon, that's also a way to get fluids in if they are not drinking well.
Sometimes despite our best efforts our sweet hens continue to decline and they are suffering. If she does not improve and you think she is in pain, it would be a kindness to let her go.
If you happen to lose her, sending the body for necropsy will give you more insight as to what the problem is. Alternatively if you can do your own informal investigation, look inside at the organs, reproductive system, gizzard and crop a lot of times you will be able to see what happened yourself. We can help you with what you see if you post photos.
Just my 2¢