First of all, your aunt is NOT the executor, (we call them Personal Representatives in Michigan), unless and until she has been appointed by the court. If she has filed the Will with the court and sought appointment, she would have priority, if she has been nominated by the decedent in her Will. So she can likely obtain appointment without anyone else's consent. You can check the probate records online in many Michigan counties, to determine if an estate has been opened or not.
Once an estate is opened, she has 14 days to notify you of her appointment and to provide you with a copy of the Will. Once this is done, you can file objections with the court and ask that she be removed as Personal Representative. If there are good reasons why she should not be appointed, this can work. If not, the judge might well defer to the terms of the Will.
Given your aunt's behavior thus far, you may want to consult with an attorney to see what your rights and options are.
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Attorney Frederick is correct and you can find out if she filed the papers yet by checking online with the county probate court where she lived. If its Wayne County go to wcpc.us and click on the case access tab and put her name in to check. If she does not start probate she has no legal authority under a will.
The other attorney answers are correct. You might also try to find out who was your Grandmothre's attorney. He may have a copy of the will or even the original. Anyone with an original will must file it with the probate court on notice of the death of the maker of the will.
Anything that your aunt does with the court is public information, and the other heirs/beneficiaries have the right to have proper notice of hearings, to attend hearings and to receive copies of documents she files with the court, including the will.
You need to consult with an attorney to determine whether you stand to gain anything by objecting to your aunt acting as personal representative, and whether the costs of fighting her would outweight what you stand to gain. Additionally, you need an attorney to help you determine if any of your (or your relatives') rights have been violated.
Finally, even if your aunt remains as personal representative, an attorney can help make sure that things are done properly throughout the administration of the case, which can take up to a year or more. But you don't want to find out you were entitled to an inheritance you didn't get, and then try to go after the person who did get it to make them give back the money (it will probably be spent by the time you try to go after them).