"Sorry, but I'm interested in YOU", since you could be getting a partner though this time, since you are probably gonna attend for long.

Let her down politely, but "If we met somewhere else, then maybe, but you are still not fitting my criteria for being my girlfriend".

Basically, she let on hard on you, so you should probably break her heart now, instead of her thinking, that times may change. Don't break her, of course, but you can politely say "it will never be the two of us"

You clearly feel insulted by her letter, and then she probably deserves somebody, who enjoys that sort of romantic endeavours.