Lucy Wagner is the daughter of Mary's Danish bassist Chris "Wag" Wagner and Kim Davis-Wagner, Tamra Davis' sister.

In 1998, at the age of 3, Lucy Wagner broke into the music business when she provided vocals on the Beastie Boys song "Peanut Butter and Jelly." There has been some speculation that it is also Lucy on "And Now a Word from Our Sponsors...", which is Mike Diamond's track on the Bape Sounds compilation album. We have been unable to find any facts to substantiate the rumor.

It is interesting to note that when Mike Diamond co-hosted Much on Demand (on Canada's Much Music television station) in the fall of 2000, he mentioned Lucy's early home demos. "My niece Lucy has recorded two Britney Spears' songs. Her father downloaded them on the internet, and then she did, you know, vocals home studio-style".

Tamra Davis honored her niece by naming the lead character in her 2002 film Crossroads, "Lucy Wagner." The role was portrayed by Britney Spears.

In August 2009, Lucy appeared in an episode of Tamra Davis' internet cooking show, making a tempeh reuben sandwich with her aunt.