Hi again, and thank you for the additional information!
The foods you're feeding may have something to do with the problem, as Whiskas and Meow Mix are foods that contain a lot of 'fillers' like corn, and other 'cereal' type ingredients which can make her stools hard and dry. Also, the change in foods may have affected her. Some better food brands you might like to try are Nutro, Wellness and Felidae. They sell these in Petsmart and other pet supply stores. She also may have a hairball problem or other intestinal obstruction which is not allowing her to pass a stool.
Can you get some mineral oil, plain canned pumpkin and hairball remedy called Laxatone or Petromalt? The hairball remedies are available in Petsmart, etc.
Mix 1 teaspoon of mineral oil into a small amount of canned cat food twice daily; mix 1 teaspoon of canned plain pumpkin (NOT pumpkin pie filling) in with her wet food, but not together with the mineral oil--at a separate feeding, also twice daily. Squeeze a two inch strip of Laxatone or Petromalt gel onto her front leg right above the paw, for her to lick off. If she's not drinking that much, try dropper feeding her water--one dropperful every 20 minutes for an hour. Also, give her more canned food than dry at this point, as it contains moisture.
All these things should help her produce a bowel movement soon. If she still hasn't gone after you give her all these remedies (give it about 8 hrs. time), definitely bring her to the vet for treatment (they may do an enema--but don't attempt this yourself!).
Please keep me posted on how she's doing. Thanks!
Cher
If my answer is helpful please click ACCEPT. Click reply for more info. Please talk to me before considering leaving neg. feedback; my only goal is to provide helpful answers. Thanks!