Based on her signs, our main concern here is inflammation and irritation of the lower GI or colon. Since Nikki has no pain or sores, issues involving the anal glands would be less likely here. Instead, we’d have to consider issues like inflammatory or bacterial colitis, whipworms, protozoal infections (ie Coccidia, Giardia,etc) and in some cases we can see this secondarily to dietary or stress induced sensitivities.
Now in her situation, we'd want to try some supportive care to rule out and address some of these signs. To start, if she hasn't been wormed recently, then it would be ideal to do so at this stage. Ideally, we'd want to use a good quality broad spectrum wormer (ie Milbemax, Drontal, Panacur), which you can get over the counter for her.
Further to this, do consider putting her on a light/easily digestible diet. Examples of this would be boiled chicken, scrambled eggs (made with water and not milk),meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used in cases like Hill’s I/D or Royal Canin’s sensitivity. This should be offered as small frequent meals and can reduce loose stool and soothe an inflamed GI. If she settles with this diet change, you can change her back to her normal food but do wean her back slowly to avoid relapse.
Finally, I would note that since an imbalance in the gut's good bacteria and overgrowth of pathogenic bacteria can trigger bacterial colitis (and this would also explain the odor change), it can be of benefit to support her good GI bacteria. To do so, there are a range of cat probiotics and GI supplements on the market. The one I tend to use for general GI issues if Fortiflora or if my patient has less then ideal stools as Nikki does, then I find Pro-pectalin, Fast Balance, or Protexin Prokolin helpful. These last few are GI microflora supports but also has a safe anti-diarrhea (kaolin) to slow the diarrhea and prevent secondary nutrient or hydration loss. These are both available OTC at vets, some pet stores, and even Amazon. So, these would also be a consideration.
Overall,these would be our concerns for the signs you are seeing. Therefore, we’d want to take the above steps to see if we can soothe her gut and settle this for her If you do try these but do not see this settling within in 24-48 hours, then we’d want to consider following up with her vet. In that case, you may want to bring a fresh fecal sample for your vet to send to the lab. This can be checked for common parasitic, protozoal,and bacterial causes for her colitis. Depending on which agent is present, your vet can dispense treatment (ie antibiotics, anti-protozoals, etc) to treat this effectively and settle it for her.
I hope this information is helpful.
If you need any additional information, do not she hesitate to ask!
All the best,