You are correct that the expenses of the estate should come from the estate. You should consult an attorney in your mother's area to make sure you have the exact provisions of the law.
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Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on since each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship. A lawyer experienced in the subject area and licensed to practice in the jurisdiction should be consulted for legal advice.
The point you raise may not be a moot point. If you sister was appointed Administrator of the estate (by the way, did your mom die a resident of NJ or another state?) then the estate probably has assets. If you are a beneficiary of the estate, your sister has to account to you. On the settlement of the account, you can raise your claim.