hmm, let's think about explainations -
1) She's actually peddling porn to perverts that she's playing against
2) She's a solid player and had way more than $20 in her account.
3) She's on the rush of all rushes. 20 --> 40--> 80---> 160---> 320 ---> 640 ----> 1280 ----> 1800
I'm going to go with some variation of all 3

It's nice of her to xfer money back to you though. More poker chips anyone???