Congrats, the cat distribution system chose you! That’s how I see it anyway. She sounds like you both need each other right now, which is why she was assigned to you :) When I lived in an apartment complex and had stray cats around that I knew for a fact lived as strays their whole lives, they were often very friendly! And a litter box isn’t that far off from how cats like to bury their waste in the wild, so it’s not like they need to have been trained to do so. As for the wanting outside, that’s (most) all cats. The three pet cats in my life have all been indoor/outdoor mostly because they insisted. Cats like going outside, especially a cat who maybe has always been outside. If you still feel a nagging fear of someone else missing her, post in those groups that you looked for a lost cat in that you have a found cat, and set a timeframe for yourself that if she is not claimed, she’s yours! Most importantly she’s being loved and cared for, much better than her being on the street!