Petition for Order and Assignment is one option, particularly if you were the one who paid funeral expenses. If you were NOT that person, then the court will order that that person be reimbursed, first, before anyone else gets assets.
There is a non-court small estate procedure in Michigan, which may get you what you need. The form is located, here: http://courts.mi.gov/Administration/SCAO/Forms/courtforms/estatestrusts/pc598.pdf
If there is an active dispute with the Agent, (whose legal authority terminated upon your sister's death), then you may need to consult with an attorney.
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DPOA is invalid after death, it expires at time of death. If this individual is not allowing access you should open up a probate estate ASAP. Contact a lawyer quickly. We would know what to do to preserve the assets.