Tula the owl still refusing to eat

More than two weeks after I rescued Tula the barn owl, she is still refusing to feed herself. Whatever food I put in her cage she just ignores it. So almost every evening I have to force-feed her. My sister helped once or twice, when she visited. Here she is feeding her mincemeat with tweezers.

She also gave her water through a syringe, as there is no evidence that she drinks by herself from her water bowl.

A week later I am still having to force food into Tula's mouth almost every night. Some nights I just put food in her cage, but she always ignores it. After forcing her to swallow a mouthful of mincemeat she squints up her eyes and appears to either be in great pain or asleep. It seems to be very exhausting for her to swallow. I just cannot work out what is wrong with her. But amazingly she is still alive! She is quite weak and light so I am very hesitant to release her, especially without knowing what the problem is. If only she could tell me...