If a process server is unable to locate her, you can petition the court for alternative service. The court will typically require you to send notice to her last known address, post at her last known address and publish.
Although this issue should have been addressed in your divorce decree, it is not too late. Since you do not agree, you can file a motion for contribution towards transportation expenses and request the court to intervene and decide the issue. Often, the threat of filing the motion (and expense) is enough leverage to make the other party more reasonable.
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In Michigan it only takes one person to get divorced. In your fact pattern, your spouse will likely file a motion for entry of the Judgment of Divorce. Provided it complies with the court's ruling, it will get entered.