Just started my slog with our friend Lewena. Currently I'm at 77 wins against her, and I've received Four Terra Bradford's In that time, so about a 1:20 drop rate for THAT card based on my small sample.

I average 5-8 wins per window. The trick is being able to play through bad hands fast, to get to the ones that give a win. The play to the upper left to bait her is the only real strategy that one can bring to bear upon this NPC. You just have to keep playing hands, and you'll see some wins.

The depressing part as those above noted is seeing win after win with nothing dropping. The drop rate on her is clearly pretty tight, and the others two cards are probably rarer.

Mostly I have been thinking of this as a long term MPG farming run, thanks to alternating with King Elmer when Lew's window goes down. I make a few thousand coins a cycle, and if Elmer drops Bahamut then thats a 600 coin bonus.

Good luck!