According to Snopes, she didn't resign but changed to inactive status. Apparently this procedure allows a lawyer who is not practicing to pay lower bar fees and avoid continuing education requirements, while keeping open the door to practice later. IIRC Snopes also said that Barack Obama did resign his law license.
It is accurate to say that both accepted inactive status rather than face inquiry. Quite common for lawyers who take a step too far.
In Michelle's case, it was Insurance Fraud and it was apparently mitigated by her ignorance of a client's actions. In Barry's case, he was challenged by another lawyer on the grounds of an untruthful application (He denied ever having used another name ....an "alias." Conveniently ignoring the Soetoro and the Dunham handles on record. Although it wasn't mentioned, he also denied traffic violations and drug use. And now, there's the SSN kefuffle. all rather significant "gaps" in the legal game.)
Michelle should have less trouble "reactivating" than Reggie Love's boyfriend.