Sounds like a cecal poo, which is normal, especially if it's smelly. Keep an eye out for a firmer poo, or at least, one that doesn't look quite as creamy (pardon the description). 2-3 times a day birds empty their ceca, vestigial loops in the digestive system. There are different species of parasites that inhabit the ceca v. the intestines. The behavior you're describing sounds a lot like worms. If you just can't find any other symptoms, that's what I would assume is the issue. You'll have to decide what kind of wormer to use. My current favourite is Eprinex, it is not labeled for use in chickens. Ivermectin is my next choice, it too is not labeled for use in chickens. Both Eprinex and ivermectin are broad spectrum wormers which can be used topically or internally. Wazine is labeled for chickens, but only kills roundworms. Use the BYC search function and google to get more opinions on these products before you make a decision. There are withholding times for these products, but since she's not laying, you likely won't have to worry about it.
When you feel the crop, it should feel soft and sacklike, not too pendulous. It should be full in the evenings and empty in the mornings, but never hard. It's really difficult to miss an impacted crop. Often they stick out so far that they're visible. 5 months is pretty close to laying age, which could be the problem. Regardless, a wormer is unlikely to hurt her.