I think it's a reasonable question, many times anyway, to ask why God may not stop something when we know His ability. There is nothing wrong with contemplating why there is evil, what is evil, and why God grants us free will to go wrong when He knows what is right.
I'm not saying there isn't a perfectly sound answer to these -- in fact, most of us here have talked about this and seem to have an agreement on why this is...but it's still reasonable to ask and dive into, without the motives of the questions being a sense of blame.
Not saying the question is not valid, though the wrong question. I ask God lots of stuff that normally turn out to be in scripture somewhere and perfectly clear.
To ask why God did not help, is saying God is at fault in some way.
The Person that did the molesting has a free will. That does not stop God from Protecting the child though, and can is more than able to do so.
So, since God could have done so, the question is not why God did not. But why God could not.
One lady we know had some guy take her 3 year old daughter who was sitting in the cart at the store. He rolled the cart outside to his van and tried to pull the child out of the cart. He pulled, moved the girl around, pulled some more and He could not just lift her out of the cart. That girl was supernatually tied to that shopping cart.
When they ran out of the store they saw the guy still trying pull the girl out of the cart and he saw them coming. He pushed the cart away, jumped in his van and took off.
The Police were able to catch him as they got a description of the van and plate.
another lady I know was watching her 5 year old play outside when the neighbors pit bull got loose and grabbed the child by the throat. She saw the whole thing and yelled, In the name of Jesus, that dog can't hurt my child.
The dog takes off with the child, jaws firmly around the neck of the child and the women ran out to chase the dog.
The dog flopped that kid all over the place shaking it's head with teeth firmly around the kids neck. The owner came out and the dog let the child go.
Not a tooth mark or even a scratch on the kid.
So the question is not why God won't, but why God can't.
Blessings.