In California, assets held in trust for a person (beneficiary) where a third party is the trustee for the trust cannot be levied upon by judgment creditors of the beneficiary while the assets are held in the trust. This is why many parents place assets in trust for their children even though the children are adults because the children cannot handle finances well and get themselves in financial trouble.However, once an item is taken out of trust and given to the beneficiary, it can be levied upon by a judgment creditor of the beneficiary.If you hold the power of attorney over your sister and you have broad powers, you most likely can assign her social security checks to pay her medical bills assuming the power of attorney allows you to do so.