Although I'm not super experienced with crop issues, I have had a guinea hen have crop issues. With mine, her crop wasn't emptying and most likely was impacted. It sounds like your guinea might have sour crop. Some people massage the crop and give their chickens coconut oil, but I'm not sure if...
Did you check the bottom of the foot and the toe pad for a brown-ish scab? Are your guinea hens overweight? If so, that maybe could lead to swollen feet.