Likely they will be successful in obtaining a lien against her estate. To calculate what you get from her estate you must take her total assets minus total debts. There is no "protection" for you and your sister against her debts because you are only entitled to what is left over after her debts are satisfied. The only time credit card companies can be forced to take the brunt of the deceased's debt, is when the estate is non-existent (no value).
From a relevant article:
"The debt is passed to the deceased person's estate and the estate is responsible for paying the debt. If there is not enough money to go around for all of the debts, then the creditor's are notified that the estate is insolvent and they have to write it off. They may still try to collect from a spouse or from the executor of the estate - telling lies that the individual is responsible when they're not. Keep in mind that this type of behavior is their charming way of trying to collect."
<< quoted from here (click).
From another site, I gather that if there is a joint owner to the home, that owner's half of the home is untouchable. Additionally, the cc company would not likely go after the home in that instance because of their inability to sell a 50% stake in a home.
(click here for source)