I agree that that poop is not unreasonable considering her problems and that mostly fluids with fine particles will be passing through her crop. The yellowish patches are probably cecal poops. It is definitely time to move on from just liquid feed and massage if it has not cleared and the docusate sodium (dulcolax without stimulant ) is a good next move. I would also start doing research on crop surgery as you cannot afford to let her get too weak. You also need to make sure that, during yard time, she is not ingesting more fibrous material, because it becomes a bit of a habit with some of these birds. I ended up doing surgery on one and had to keep her in a box with incontinence pads as bedding or she would eat whatever straw, hay, grass or shavings she had access to. As soon as she recovered from surgery and I was able to put her back out with the flock I witnessed her eat a blade of straw within 10 mins of being in the pen. She impacted again 4 months later and very sadly, I was unable to save her a second time despite my best efforts.
Hens will only lay eggs when they are up to weight and have sufficient nutrition to produce them. You are right that her lack of nutrition is why she is not laying and nothing to be concerned about in itself. The pullet that I did surgery on was pretty emaciated but she was eating normally within 10 mins of gluing her back together and back up to weight and laid an egg exactly 2 weeks after surgery..... I removed a soft ball sized mass of soggy tangled vegetation from her crop that nearly weighed more than she did (bantam cochin/pekin) It was quite an eye opener and certainly had no chance of passing down through her system or being regurgitated, so surgery was her only hope, but you never really know that until you open them up.
I wish you luck and if the dulcolax is not successful and you feel that you could do the surgery..... it is not difficult but no good if you are squeamish.... feel free to give me a shout as I have a few tips that may not be covered in some of the You tube videos that are out there.