Hi, there could be many causes of your cat being so quiet. First off, it's a good sign that she's still drinking and eating. Usually, when they're sick they hide and won't eat or drink. How long have you had her? How much weight has she put on? If she's eating a lot and not putting on much weight, it could be worms, diabetes, or overactive thyroid. Since she was a stray, the odds are that she has worms-especially, if she's thin but has a big belly.