Dress as a boy? Oh, NO! Not that! Play up your obvious feminine wiles, deary. Curl your long tresses about your face, but wear a "Barbossa-ish" hat with showy feathers. Gambling with cards is as much game of intimidation as it is actual skill. Your real goal is to either blind them with briliance, or baffle them with bullsh*t. If they're entranced with you, the cards really don't matter. Savvy?
And for a name, maybe something rougher, like "Fox McGrath"? A bit of a roll off the tongue to it, to make the gents think twice? And puff up a bit as you say it? Yes, quite intimidating you'd be. :)