She landed her first acting job in the 2005 independent film Boo. She later won the role of Georgia LaMarque, a French girl whom Bo and Billie had been falsely led to believe was their daughter on the NBC soap opera Days of our Lives, but only appeared in five episodes. Months later she took over the role of Chelsea Brady (originally portrayed by Mandy Musgrave). She and her dog were seen on The Tonight Show with Jay Leno, when she was randomly interviewed at a gas station for a segment. Melvin has also guest-starred on Summerland, Jack & Bobby and 8 Simple Rules. With her family, she has also appeared on Family Feud.
In 2010, Melvin starred as Kaia in Seven Deadly Sins which premiered on Lifetime alongside Dreama Walker. The 1st part premiered on May 23 while the 2nd part premiered on May 24, 2010. In 2011, Melvin appeared in episodes of House M.D. and Castle.
In 2014, Melvin appeared as Penny Pinchelow in Dumb and Dumber To, portrayed Mary in Zombeavers, and Sarah in the drama thriller film Madtown.
She will appear in the upcoming and final season of MTV's Awkward.