One of my hens has sour crop. Off her food yesterday, last night I picked her up to check her over and clear liquid came out of her beak. This morning picked her up again and her crop was full of liquid and squishy. Have massaged it whilst holding her upside down, a lot of gunky liquid came out. Have given her some natural live yoghurt, is there anything else I can do? Have also bought some grit this morning to prevent it happening again. The other hens have had some yoghurt too. Is there anything else I should do for her?