Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 16 years of experience. I look forward to working with you.
This is quite concerning, especially if she has not had anything to eat/drink in a few days. On the one hand, this is an emergency situation and I must recommend you take her to be seen on emergency today. If your veterinarian has an emergency on-call option, then I recommend you take this and call.
Second as to the cause, this could be related to an infection which can sometimes occur post-operation (intrabdominal or entire body), or it could be related to a bleeding disorder which is causing her to be anemic. Or sometimes we see anemia from other causes (immune-mediated hemolytic anemia) which occurs in the blood secondary to stressors or activation of a blood parasite some cats have. Or she could be have a post operation organ problem (liver, kidney); sometimes depending on the pain relief administered there can be liver/kidney side effects from this which is why a check of this is critical. There are certainly other possibilities but she really must be examined and then have some blood testing (CBC, chemistry profile, urine check).
At home, you should continue to tempt her to eat with all of her favorites (bring out the canned cat foods, canned meats like tuna and even try people baby food). However, given the length of time she is not eating, I am worried this is not going to get better on its own. There are no safe over-the-counter drugs I can recommend that will help this situation.
I am at a point I need to know what questions you have. I hope that the information I provided has been helpful.
Please let me know if for any reason you need further clarification, have more questions, or were expecting a different type of answer.
My goal is to provide the best answer possible prior to you leaving a feedback rating.
If you received all the information you needed, then kindly submit a rating.