Mary Mayes had faced a lesser charge of conspiracy to commit kidnapping.
According to court documents, authorities now believe that Mayes confined 12-year-old Alexandria Bain and 8-year-old Kyliyah Bain after her son and daughter-in-law took them from their Tennessee home to Mississippi.
In court on Tuesday, Mayes' attorney said he did not know specifically what his client is accused of but he speculated that prosecutors might believe she restrained the girls in some way.
Mayes' bond was increased from $300,000 to $500,000. Her preliminary hearing and that of her daughter-in-law, Teresa Mayes, was rescheduled for June 19 pending psychological evaluations of the two women.