What happens if you have more than 1 apple id associated with 1 account...?
I understand you want to keep an eye out... but all messages?  and no privacy? ;-)

That said. 

What you could try is setting up a extra account (user) on your iMac/Macbook. Hookup her iCloud account there. You can swap between your own account and 'her' account on the fly. 

When you then open iMessage on the desktop i think (and expect) that you would find all copies of her iMessages. That is, Apple iMessages, true SMS are not delivered (only on the iPhone). But since she has a iPod Touch... i think you should be safe. Give it a try.