I've yet to visit a casino that didn't have some version of a leash that you could get for their player's club. I actually ended up with 10 cards on one leash when I did a run on the strip at Vegas one year. 
I'd suggest that sis get her own card. That way, if they both want to play different things at the same time, there's no trouble. Also, when they send out the low-value players perks, they'll both get something, too. That's the way I'd do it.
^-.-^

I'd suggest that sis get her own card. That way, if they both want to play different things at the same time, there's no trouble. Also, when they send out the low-value players perks, they'll both get something, too. That's the way I'd do it.
^-.-^

. Also make a point of signing up at every casino you go to (keep in mind many share players clubs so don't waste time in line at sister properties) the little coupons you often get are gold for the light gambler (learn how to use a "match play" well and you find yourself with an extra $5-$25 in your pocket more often than not).
That's right, my wife and I got to stay in a room usually reserved for celebrities absolutely FREE.
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