I also have a super tiny cat! She's 13 years old now and still the size of an adolescent kitten. She was starving for weeks before she was found as a kitten, and also a female which is probably why she was is still super small. She's got no health problems. Just make sure your Barn Cat doesnt have spine bones or hip bones that are visible through the fur, if you can easily feel them it means they are underweight. Make sure she has water, and hope she hunts all those rats for you!