My cat won’t eat cat food

I have this cat that won’t eat any cat food we give her, she drinks milk(kmr) but that’s it, I’ve tried mixing the milk with cat food both wet and dry but nothing will get her to eat it., she mostly lives outside so I’m guessing she is eating something out there since she isn’t as skinny as when I found her but still, is there any way I can get her to eat cat food? ( I’ve taken her to the vet and there are no internal problems)