You have a very complicated situation, and you really should see an attorney to address this in more detail. From what it sounds like in your summary, your step-mother would be considered a "pre-termitted spouse". Michigan law changed the way that it dealt with such heirs, about 10 years ago. If there is not evidence that your father *intended* to exclude his wife, she would be entitled to "elect against the Will." She would be entitled to about half of her intestate share of the estate, (the amount that she would have received, if your father did not have a Will).
This would be approximately $65k, plus 1/4 of the rest of the estate. She would also be entitled to exemptions and allowances worth up to an additional $60k. The former amount would be reduced by 1/2 of the value of any assets received by the spouse as a result of the death, by other means, such as joint property, beneficiary designations, and the like, if any.
The answer is also subject to change, based on the title to the assets. If the assets were titled jointly with the spouse or she was designated as the beneficiary, then there would be no estate, and it would not matter WHAT the Will says.
Best of luck to you!