McMahon was at Camp Pendleton doing paperwork to officially change her last name when she vanished on March 31. Reid also left his post at Miramar Marine Corp Air Station.
McMahon's family had feared the worst, saying she had called friends and relatives recently, upset after disputes with her husband, a fellow Marine whom they had never met.
Military authorities originally suspected that McMahon was abducted, but later said there weren't any indications of foul play. Investigators tracked down one of the couple's stops in Kansas, where McMahon was seen on a surveillance camera trying to withdraw money from an ATM.
In addition to the video, Newsday reports that the family learned both McMahon and Reid had updated their MySpace pages. Maggie's sister, Heather, told the paper that her sister called her Wednesday.
Heather McMahon said her sister said she left the Marines because she'd been suffering from anxiety.
"She said it was just too much for her," Heather McMahon told Newsday.
The couple wouldn't reveal where they are, but Heather McMahon said her sister is making plans to surrender to authorities.
"They didn't think it was going to be that big of a deal," she told the paper.
