I agree with the others, another 3yr old touching her will not cause this type of behaviour in her something else is definately going on especially if she did not want to get into the tub. Remove her form that school, I say.
I agree with RockRose. There's something else going on here. I just reread your post and realized that you said you found out this girl touched her again AFTER you called back. So they didn't inform you until you called THEM.
I would hate to think it was an adult that touched her there, but again I don't like the way the school's handling it.
If it were my child, I'd take her out of that school. At the very least, they are not properly watching or seem to care about what the kids are doing. You need to do whatever you can to protect your child.
Charisca - something else is going on here.
A 3 year old touching another 3 year old on the genitals two times, a week apart, will not cause this kind of panic.
Are you sure the nightmare was related to the touching, or was it a typical night terror (child isn't awake) or nightmare (child is awake and aware)?
I agree you need to recontact the school, but at this point it's EXTREMELY important that you not overreact because the more strongly you react, the more strongly she will.
While this isn't the kind of thing you want to ignore or promote, children touching each other a couple times is normal, and doesn't usually cause great distress in the child.
Best wishes.
Is this a preschool? How old was the other child? And where was the supervision over these children when this happened? Do they even know what happened? I don't like the nonchalant attitude they have here. They should take this seriously and have a talk with the children and both parents. You need to feel your child is safe in their school and if you can't feel safe there, put her in another school.