Once you are listed as a creditor on a bankruptcy and the debtor gets a discharge, you are no longer legally entitled to collect the debt. The debt doesn't exist, at least not legally, and if you tried to collect it you would be violating bankruptcy law and subject to penalties.

Your sister can of course opt to pay you back but it would be purely voluntary on her part. Because this would be voluntary, there is no point in drawing up any legal documents to enforce this. All you can do is sit back and wait and see if she does pay you back. Going forward you can refuse to lend her any money in the future and you can dissociate yourself from her socially if that gives you any satisfaction.

Be aware that in order to get a bankruptcy discharge your sister had to provide the court with a budget that left her no excess money that could have been used to pay back her debts, so the act of her coming up with extra money now to pay you back might contradict her sworn statement as to the budget she needed to live on that she filed with the court. (If she came into additional income, then it wouldn't be a problem, such as unexpected overtime pay or a raise that wasn't anticipated.)

In the future if you want to loan money to someone, talk to an attorney about how you might created a secured loan. As a secured creditor you will retain your right to get paid back if the item pledged as security has at least the value of the loan you made. Anything can be used to secure a loan - a car, a house, jewelry, electronics, personal property with significant value. (If personal property is given to secure a loan, then you need to perfect your lien by taking physical possession of the property for the duration of the loan. An attorney can explain how this is done.)