Have a friend who was over 18 had sex with someone under 18 refused public defender
Pleaded guilty to aggravated sexual battery given 10 years probation fines still paying fines probation period over she is ( and was ) emotionally and socially immature is still confused about what legally transpired can she have her case heard again possibly overturned or at least apply for expungement

No, unless he filed appeals within the time frame the case is not going to be heard again.

Most states have rules to allow expungement but most will not for sexual cases and esp those with minors.

He will need to hire an attorney to first find out what their state allows and then if possible file a motion in the court where the case was heard