I don't know how long ago this crime allegedly occurred, but your daughter is an adult. Although you could certainly report the offense and it could result in an arrest, if it is not time-barred by the state's statute of limitations, if your daughter is unwilling to prosecute this man, the state will be unable to proceed. As badly as you feel about this, and I'm sure you do, basically it's entirely up to your daughter to press charges. Charges can't stick without her.
Is it one person's word against another? Well, if she went to the police right away and a rape
kit were taken, then there would be evidence. But if any time has elapsed and no evidence was collected, it would come down to a matter of credibility. Again, however, your daughter is the complainant. If she wants to leave things be, that's what you should honor, though you might wish to steer her towards counseling if necessary.
In most states, there's a long statute of limitations on sex offenses. So perhaps with some counseling she might change her mind down the road and eventually be ready to bring charges here.
Edited by FranL on 7/2/2010 at 12:23 AM EST