MAGI is adjusted gross income (AGI) plus tax-exempt interest, Social Security benefits not included in gross income.
yes, she opens an IRA account at a financial institution and makes a contribution. You report the MAGI on the Medicaid application based on her tax return amounts. Note that she must have earned income to contribute and if she has an employer retirement plan her contribution could be limited. If over age 50 she can contribute a maximum of $8,000.