Hello,Peanut butter is not toxic to cats. But, in large quantities it can cause diarrhea or vomiting. If she develops diarrhea, this is what you can do:1- Do not give things like Pepto Bismol it is toxic to cats. 2- Leave her without food or water for 8-12 hours. Then, change her diet to rice (50%) and boiled boneless chicken or ground beef (50%) until the stool is back to normal then wean back into regular diet.3- Supplement with a probiotic (fortiflora), these are friendly bacterias that help with regularity. Or, give 1-2 teaspoon of plain yogurt 2 times a day.Hope the above helps, if you have additional questions I will be glad to answer them.Thanks.