You aren't going to be able to get this money back through a bankruptcy. In fact, if she tries to repay you instead of her other creditors, it may be a voidable preference and the trustee could even sue you to get the money back. Your loan to your sister is dischargeable in bankruptcy just like any other general unsecured debt. Your best option might be to just file a proof of claim in her bankruptcy and hope for the best.
My answer is for only informational purposes and is not legal advice. I am licensed to practice law in Oregon and I recommend contacting a local attorney for the best help with your legal questions.
Here is the bad news: your sister is required by law to disclose her debt to you, you will receive notice of the filing and instructions to file a proof of claim if assets are recovered, you will receive your pro rata share of assets recovered if you file a proper proof of claim, and your debt will be discharged with all the other unsecured creditors. In addiiton, if your sister has made payments totalling $600 or more in the one-year period before filing, the trustee will make demand on you to surrender those funds. Nothing prohibits your sister from voluntarily paying you after the discharge, but you are premanently enjoined from requesting payment. If you receive anything other than a Notice of Commencement and request for Proof of Claim, you should consult with experienced bankrupty counsel. If you do not know one, try the attorney-finder at www.nacba.org.
I regret that I cannot offer more favorable information, but please remember to designate a best answer.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.
Unless your sister files Chapter 13 or her Chapter 7 is an asset case from which liquidation of asset(s) will yield a distribution to creditors, you will not legally be able to get a dime.
The purpose of bankruptcy is to provide an honest, but unfortunate, debtor with a fresh start. If she files bankruptcy and receives a discharge of her liability to pay certain debts, you would never be able to even ask her to pay the money back.
Advice on this forum is for informational purposes only and should never be mistaken as a substitute for legal advice. If you are in need of legal advice, you should consult local legal counsel.