If it's not your property there really isn't anything you can do, and if your birds are being eaten by her cats then it's time for you to move. It doesn't matter if she can't afford the place without you there to pay rent, there are plenty of people around who would readily replace you. Keep the birds penned up until they are fully grown, at least, or move somewhere else. I'm amazed that your landlord was OK with you having chickens in the first place, not many owners would allow that.