Welcome! Thank you for your question.
Unfortunately if the trust was a revocable living trust
then the trust is your mother's only until she dies. Your sister has no legal right to the money in the trust until your mother's death.
The only way that you sister is entitled to money in the trust or the joint checking account is for her to prove that she placed the money or asset in the trust from her sole name.
This is an unfortunate circumstance. Your mother will be ineligible for Medicaid unless your sister returns the funds. As an alternative, if she does not have the money then your mother can make a claim for undue hardship to waive any gift penalties. It is possible that Medicaid requires a lawsuit be filed against your sister before they will grant undue hardship.
I cannot provide you with legal advise. I have provided you with information about the law related to your question. My answer, and any information that you find online, should not take the place of having a consultation with a lawyer in your area to advise you regarding your specific issues.
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