I'm no expert, but I would have thought that fibre pellets would be intended to help to keep things moving. You could get some lactulase from the chemist - NI recommended that to me when Dylan was a little constipated when he was very young. Constipation would generally come on gradually, so if she hasn't been straining at all before this and her poos haven't been extra hard, it may not be constipation. So there is always the remote possibility of a blockage to be aware of. Sorry don't want to scare you, but better a worried owner than a sick dog. And I'd advise not giving any bones or chicken wings for the time being and encourage her to drink as much as possible. Let us know how she goes.