How is it possible that you were arrested without warming. Sec 498A cases always have reconcilation proceedings before a FIR is launched. She left your house on the 26th of May and an FIR was filed on the 5th of June. How is that possible ? Sec. 498A cases have to be preceded by at least 3 efforts at reconciliation or at least a notice to you that a complaint against you has been received and you are required to come and give your side of the story.
Something in your story is not gelling. Either you are not telling the whole truth or there is something fishy going on. But considering that you have already got bail, the worst is over and your options are now clear. If you want to compromise and keep the marriage going for your daughter sake, this is the time to do so. If you and your wife are able to strike a settlement either of living together or mutual divorce, you still have time to move a joint application to quash the FIR.
But, in case you have decided to go ahead with the divorce, then you are better off filing for divorce under the plea that you were mislead into the marriage by not being told of your wife’s mental retardation. Also include the FIR and your arrest as acts of cruelty. Don’t expect instant results. If your wife contests the divorce, it will take time. But, if you start the process, at least in time it will be done.