My question involves criminal law for the state of: Texas

My friend pleaded guilty for possession of meth. 32 grams with intent to distribute. They told her if she didn't plea bargain they would give her 40 years. So she did and they still gave her 20 years. Can she appeal this sentence since she is a first time offender? Can she request a sentence reduction? She is in the Texas Department of Criminal Justice system not state jail.