Is there a way to "duplicate" text messages? Meaning, can I set it up to send me a copy of my childs text messages?
If you have an iPhone, iPod Touch, iPad or Mac (with Mountain Lion) you can add her iCloud account into your iMessages settings. This would send all of her iMessages to your device just like it was her. It would also allow you to reply to them, just like you were her.
Note that this only applies to iMessages, not all SMS/Text messages - meaning you would only see messages from people with iPhones and/or people using iCloud.
Also note that if her iPhone has iOS6, she would get a pop-up message notifying her that a new device (showing the name of the device) has started using her iCloud account.
What you would see is limited to iMessages only. iMessages are only messages sent from iPhones OR iPads, iPod Touches or Macs, using iCloud and the iMessage system. In order for another device (yours) to get copies of iMessages sent to her, the same iCloud account must be configured on both devices (yours and hers).
i dont think you can acheive what you are looking for using iCloud.
You would see iMessages sent to her phone number from other iphones
You would BOTH see iMessages sent/recived to/from YOUR iCloud account
Unless you take additional steps to add restrictions and lock her out of 'account settings' on the iphone, if she starts poking around in the accounts screen, she would see your account info = BUSTED!
If she communicates with someone that does not have an iPhone, you will see nothing
No way in the stock iPhone (non jailbroke) to send iMessages to email.
Dont start asking about Jailbreaking - if you have to ask, it's far too complicated and risky.
More information about text formats