The two tips I like for e-flirting work best over AIM, but I suppose could be conducted via PM.
It's a tried and true trick.
First of all you try to find out what her idea of the best vacation or situation in the world is, like say she likes the beach. Then you vividly paint a word picture for her, of you and her at the beach. Describe the sounds, the salt spray, the sun, find out if she likes pina coladas or beer. Keep teasing out her likes and dislikes and create imaginary situations that would make her feel great. Then she will start to associate feeling great with you. Then BAM you are in. Takes work but worth it.
Second one is paint a vivid word picture of her taking a luxurious bath. perhaps you lead her into the bathroom and there are candles lit and a nice hot bacth waiting for her with lots of bubbles. You rub her neck/shoulders/feet as she luxuriates in the warm water and scents and relaxation. This associates those feeling with you in her mind, and also shows you are willing to take care of her and spoil her to a degree. That you appreciate her.
Basically lavish lots of attention on her, find out what her likes and dislikes are, and remember them well. Incorporate them into the fantasies you write for her.