It sounds as if the printer isn't setup properly for wireless printing. If your Mac needs to be be powered on and awake, then your Mac has printer sharing turned on and her Mac is connecting to yours instead of the printer itself.
Is the printer connected to your Mac via a USB cable?
OK, then my first statement is probably the issue. Check on your Mac to see if printer sharing is turned on. If so, turn it off, delete the printer from your wife's Mac, and re-add it.
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