Sardines or tuna for dinner served with the oil they come in - for the cat, not for you!
And if she is an indoor cat, dig up a good tuft of grass and put in a plant pot.
One frequent cause of constipation in cats is caused by them swallowing too much hair and getting fur balls when they are moulting. Grass usually moves things along, or working in the opposite direction brings itself and the fur ball up.
So don't walk around in bare feet or stockinged feet in the dark!
Take samples with you to the vet.