I am sorry to hear you are worried about your cat. My name is ***** ***** I will do my best to help. I am a veterinarian with 30 years experience.
If she is not eating, and is losing weight, I am concerned that she is ill. It could be many things; a good physical examination is the place I would start if I could. I would check to see if her gums are a normal pink color rather than pale, I would palpate her internal organs and lymph nodes, take her temperature, listen to her heart and lungs, feel her pulses.
She may have stopped eating from the stress of being made to live outdoors, but if a cat stops eating from illness or stress, that can cause liver disease. Not eating can lead to hepatic lipidosis, fatty liver disease, in cats and the only cure is to get her to start eating. If when she is examined there is any sign of liver disease, I would try to get her to eat by using prescription appetite stimulants like cyproheptadine or mirtazapine, or even by putting in a tube so she can be fed and medicated.
Try to encourage her to eat by offering kitten food or baby food or table food, but since she is weak and losing weight, having her examined by your veterinarian would be best. Let me know what other questions you have. Rebecca