Is she eating OK Gaynor? Are you absolutely sure she hasn'y "been" - they can sometimes hide.
Do you know if she may have eaten anything suspect, none food perhaps a bit of a that may have broken off?
What is her usual food - if you give egg and or pasta, then I'd hold off on those as they help to bind them. Try giving a bit of tinned dog food or just meat, that will often loosen them up, but only if you know none of the above apply.
Otherwise, if she starts looking off colour, a trip to the vets may ne called for.
hth