Mullins was born with fibular hemimelia (missing fibula bones) and, as a result, had both of her legs amputated below the knee when she was a year old. She is a graduate of Parkland High School in Allentown and Georgetown University in Washington, D.C.
While attending Georgetown University, she competed against able-bodied athletes in NCAA Division I track and field events. She competed in the Paralympics in 1996 in Atlanta, in which she ran the 100-meter dash in 17.01 seconds and jumped 3.14 meters in the long-jump.
In 1999, she modelled for British fashion designer Alexander McQueen in his London show, on a pair of hand-carved wooden prosthetic legs made from solid ash, with integral boots. She is able to change her height between 5 ft 8in and 6 ft 1in by changing her legs. She has been named one of the fifty most beautiful people in the world by People.
She also appeared in Dazed & Confused Magazine in 1998, seen on Coverage, and in Kenneth Cole's anniversary Campaign (2010). She is also part of the L'Oréal fashion Beauty Team along with Jennifer Lopez and Gwen Stefani (2011).
In 2002, she appeared in Matthew Barney's Cremaster 3 as a cheetah woman (the Entered Novitiate and Oonagh MacCumhail). In 2006, she appeared in World Trade Center, playing the role of a reporter. She also appeared, in 2003, in the made-for-television version of Agatha Christie's Five Little Pigs, as the woman who asks Hercule Poirot to clear her dead mother of murder.