Sue has made the best response, but sometimes cats just change. I would follow what Sue said, make any changes of eating or toileting in a notebook, including furballs being eliminated, and maybe talking to your vet after the weekend if she is no different. If she isn't in distress that should be soon enough.
I have no idea what has happened to Pippa, I haven't seen her since this morning, but she does disappear for hours, so I am trying not to worry. (Yeah right) Why do we love these strange, independent animals so much?