Born in New Orleans, Louisiana, Lemmon attended Loyola University New Orleans and continued as a law student on that campus, to receive a Juris Doctor from Loyola University New Orleans School of Law in 1964.

She was a law clerk for her husband Judge Harry T. Lemmon, on the Court of Appeal, Fourth Circuit of Louisiana, from 1975 to 1980, and she continued with him as his law clerk on his elevation to the Supreme Court of Louisiana from 1980 to 1981.

She was a Judge pro tempore, Court of Appeal, First Circuit, Louisiana, in 1990.

Lemmon was nominated by President Bill Clinton on December 19, 1995, to a seat vacated by Peter Beer.

[2] In June 2009, Lemmon was in the news as the jurist who denied a request by Mose Jefferson to delay his trial on bribery charges also involving former Louisiana legislator Renée Gill Pratt and former Orleans Parish School Board president Ellenese Brooks-Simms.