After law school, McComas practiced law at a private practice until 1983. In 1984, she joined as an Associate at the Law Offices of Bruce J. Gilbert. Since 1985, she has been a sole practitioner. In 1989 and 1990, she served as the chair of the special committee on lawyer referral for the Maryland State Bar Association. She has been a member of the Harford County Bar Association since 1983. She was a member of the Maryland Criminal Defense Attorneys' Association from 1986-88. In Harford County, she was a member of Harford County Republican Central Committee from 1998-2002. She was also a member of the Maryland Municipal League (president, cecil/harford chapter, 1989–90), and a member of the legislative committee, from 1989 to 1992. McComas served on the Board of Directors for the Sexual Assault/Spouse Abuse Resource Center from 1982 until 1989. Finally, she has been a member of the Claims Committee, Local Government Insurance Trust, since 1996, serving as vice-chair since 2002.