The young black sharecroppers were being driven along a rural road when they were stopped by a white mob beside the Apalachee River, just over 50 miles east of Atlanta.
The statue of Susan B. Anthony, Elizabeth Cady Stanton and Sojourner Truth will be dedicated in August and help mark 100 years of women's right to vote.
The mother had sought donations for the "bucket list" of the girl who she said was dying of a terminal illness.
Jarrod Ramos, 39, has pleaded not guilty and not criminally responsible, which is the state's version of an insanity defense.
Martin Fox, the former president of a private Texas tennis academy, also agreed to plead guilty to conspiracy to commit racketeering, prosecutors said.