I don’t buy it.
A normal girl (or person) doesn't forget about writing several messages.
Conclusion: She definitely must have a problem.
> OMG, how much did you drink the last 3 days??
>Oh Shit. that was your other personality?? (note to self: DON’T DATE THIS GIRL)
Then just go on normally from there.
She gives you her number. In most cases girls do that if they are interested. She adds you on facebook -- just that a guy she doesn’t remember can stalk her? Just tease her and show some self confidence.