Thank you for replying - we have felt her crop and it does feel full, but just as full as our other chucks... We have been giving her some probiotic yoghurt which she likes, but is taking tiny amounts of it mixed into layers' mash. She is still drinking, but this afternoon she has retreated into her nesting box and is just sitting in the straw. Her poos are quite liquid, diarrhoea like, and one was yellowish (but that was two days ago and the colour is now back to browny).

Will try her with the olive oil, as hopefully it won't harm her and might help...
Will keep you posted!