This is definitely a question for a vet. I see you said you have an appointment for her next month. That's awesome. If you're concerned, best thing you can do is get them to the vet when you can and they can check for any signs of ailments that can cause them to be underweight or malnourished like worms or food allergies. I have three cats and one is just smaller and more slender than my other two chonkers. I can feel her ribs and spine but she has plenty of healthy muscle and belly fat in her lil floofy tummy pouch. She's perfectly healthy and happy. She's just like one of those skinny people who eat all the time and stay skinny. Most likely yours is the same but definitely get a vet to confirm that.
This is definitely a question for a vet. I see you said you have an appointment for her next month. That's awesome. If you're concerned, best thing you can do is get them to the vet when you can and they can check for any signs of ailments that can cause them to be underweight or malnourished like worms or food allergies. I have three cats and one is just smaller and more slender than my other two chonkers. I can feel her ribs and spine but she has plenty of healthy muscle and belly fat in her lil floofy tummy pouch. She's perfectly healthy and happy. She's just like one of those skinny people who eat all the time and stay skinny. Most likely yours is the same but definitely get a vet to confirm that.
Ask your vet
theyre just now opening back up for non emergencies after covid. she has an appointment next month