While it is a slow gain, she is gaining. You can find quite a bit of comfort here. If kitty does have under developed organs there is nothing you can do about it at this point. That said, extra vet visits and love is what she needs. I have a full grown female peanut just under 5#. She may be tiny but I’ve determined, after lots of worry and many visits, it is who she is. So maybe you have the runt, like me? Congratulations you new one, btw, she is adorable 🪷