I'm sorry. You did a good thing. You invested money and time and your hopes in this girl, to give her a better chance to build a better life for herself, and it didn't work out as you had hoped. Of course you are disappointed and angry.
This situation reminds me of my second-favorite line from Buckaroo Banzai: "No matter where you go, there you are." The small town may have been a contributing factor, but the underlying cause of her problems is her. She needs to change that before anything else will stick.
This doesn't mean you should write her off, or turn your back on others in this situation. You have given her a shot to get out; she was not mature enough to take advantage of it; but maybe in a few more years she will grow up, realize that there are other places with better opportunities, and be ready to try again.
The key is not to offer what you can't afford to lose, whether that is time, money, emotion, etc. Generosity of spirit is an amazing thing, and it makes you a special person. But it needs to go along with firm boundaries and limits so you don't get taken advantage of or become jaded/cynical. You need to be able to offer whatever you offer as a gift, without being invested in how the recipient uses that gift.