You're trying to problem solve this logically. You need to look at it the other way around. She says you already approached her. That could mean couple of things.
a) it did not go well
b) it went ok but she is not interested
c) it went well, the interaction and conversation but she shot you down
d) it went any of the way but at the end you made it awkward
If she said you two already *talked*, that could at least indicate that it went ok and she kind of remembers that.
At the end, you cannot tell because you do not remember. The truth is you probably do not remember because (now I am assumin) you either have a bad memory, or all the girls look super similar, or you quickly forget girls who it lead nowhere with.
The question first has to be, not what do you say but what is your goal? I would say pick her up if you approached her.. at which point this "you already approached me" is all you have. And you do not know where you actually are, because you do not remember the previous conversation. So answers to that could be numerous, but you'd be shooting blind. So saying something like "see? Now you have a second chance, it's your lucky day!" and one girl may laugh and the other immediatelly take of.
So I would go the other way and get at least some info about the past interaction.. but nothing too deep. So a simple "is that good?" or repeating with upward intonation to give her the "expand on that please" like "I already approached you?". Because to be frank, it would be for benefit of all if you remembered. Any gamey stuff is just.. I don't see the value. Act like a human being.. most of us would be confused if something like that happened
