I love the idea of borrowing money. Best defense is attack! If you do that she wil freak out! Maybe you should talk of an old uncle in manilla that needs surgery.... Or maybe talk about your mom who died for the 3rd time, poor her!
.... Oups sorry heard that story before!
Bottom line is you may not be able to completely get rid of her so telling the so you have a crazy person sms ing you should work, but this is a 1 shot solution, no repeat accepted!