South Carolina coach Dawn Staley said the NCAA also denied the school's appeal after the initial decision and that Littleton was "devastated" by the decision.
Littleton will practice with the team this season and have two years left to play with the Gamecocks.
The 5-foot-9 guard from San Diego was a McDonald's All American in high school. She played 33 games for Texas a year ago, averaging 8.4 points and shooting 32.3% from 3-point range.
Staley had hoped Littleton could add some experience to a team with six newcomers.
The eighth-ranked Gamecocks open the season Tuesday night against Alabama State.