A lawyer for Janet Jenkins filed an emergency motion for contempt for not surrendering the couple's daughter, Isabella Miller-Jenkins, on Friday.
The motion seeks court sanctions and the assistance of law enforcement in locating Lisa Miller, whose last known address was Forest, Va., but whose whereabouts are now unknown.
"I am so worried about Isabella," Jenkins said in a written statement issued by her lawyer, Sarah Star. "I do not know where she is or whether she is okay."
Miller's lawyer, Mathew Staver, didn't immediately return a call seeking comment.
Miller and Jenkins got a civil union in 2000, and the girl was born to Miller after a pregnancy that began with artificial insemination.
They broke up a year later, and Miller moved to Virginia, setting the stage for a custody fight that has been closely watched by gay rights advocates, as well as conservative religious groups.
Courts in Virginia and Vermont have ruled in favor of Jenkins, even though she is not the biological mother. The U.S. Supreme Court declined to hear arguments on it.
The court filings Monday were made in family court in Rutland, Vt.
Judge William Cohen, who granted the couple's civil union dissolution and has presided over the custody battle since, didn't immediately rule on the contempt citation request or set a hearing date, court officials said.
A year ago, in ruling against Miller's bid to deny visitation by Jenkins, he warned Miller she risked losing custody of the girl if she continued to violate orders. On Nov. 20, he made good on the warning, ordering the custody change.
Jenkins' lawyers say their concern is the girl's safety.
"My goal has never been to separate Isabella from Lisa," Jenkins said in her statement. "I just want Isabella to know and love both of her parents. I just want to be with her, like any parent."