One problem is that the girl, given the name Maria, appears to be 5 or 6, the Kansas City Star reported. Lisa Irwin, 10 months old when she disappeared, is a month away from her third birthday.
Deborah Bradley, Lisa's mother, said the little girl was big for her age.
"At first I didn't think it looked much like Lisa, but then after comparing pictures of Lisa and with her, I started seeing major resemblance and then the height and weight threw me off," she told the Star. "And then we were like, oh my gosh, this really could be her."
Maria was discovered living with a Roma couple -- members of the group formerly known as gypsies. DNA tests have shown the couple could not be her parents.
The FBI said it is working with investigators in Greece after getting calls remarking on the resemblance between Maria and age-advanced pictures of Lisa Irwin.
"We are following up on those calls by reaching out to the Greek authorities just like we would with any investigation by reaching out to our law enforcement partners," Bridget Patton, a spokeswoman for the FBI in Kansas City, said.
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