When her brother Chester A. Arthur became president, she lived in the White House during winter months to host social events and care for her niece.

As acting first lady, McElroy ended the tradition of suspending social events during Lent, and she held large weekly receptions.

[1] Malvina's family was primarily of English and Welsh descent, and her grandfather, Uriah Stone, fought in the Continental Army during the American Revolution.

[2][3] Her father, William Arthur, was born in Dreen, Cullybackey, County Antrim, Ireland; he graduated from college in Belfast and emigrated to Canada in 1819 or 1820.

[4] Her mother met her father while William Arthur was teaching at a school in Dunham, Quebec, just over the border from her native Vermont.

[7] McElroy accepted the position, though she faced some reluctance, as she was a naturally shy person, and it would require her to leave her family in Albany.

[11] McElroy quickly learned the responsibilities of White House hostess, and she described herself when starting as "absolutely unfamiliar with the customs and formalities".

[11] When the winter social season ended in March, a farewell dinner was held in her honor, and she returned to Albany.

[7] McElroy then broke with the tradition of suspending social events during Lent, and she held weekly open-house receptions in the spring during which a hostess would be assigned to each room, culminating in an elaborate luncheon in the family quarters.

[6] McElroy presided over many events and honored former First Ladies Julia Tyler and Harriet Lane by asking them to help her receive guests at the White House.

[7] Her final reception took place on February 28, 1885, one week before the end of the Arthur administration: 3,000 people attended (including Adolphus Greely), and 48 daughters of officials and the social elite assisted her.

[7][14] During the presidential transition period, McElroy befriended her successor Rose Cleveland, who would also be the sister of an unmarried president.

Before McElroy left to return for Albany, Senator George H. Pendleton and his wife held a farewell reception in her honor.

McElroy and her husband were supportive of civil rights for African Americans and hosted Booker T. Washington at their home in Albany in June 1900.