To assume makes an ass out of U and me.
To all intents and purposes, unless her V5C shows her correct and current address, the date of any notice sent to an address other than the address on her V5C is irrelevant for the purposes of the requirement to serve a NIP under s. 1 RTOA 1988.
If you check the vehicle status on the DVLA's website, it will show when the latest V5C was issued. That should give a clue as to what address is showing on it - although we generally take the pragmatic view that unless the OP has the V5C in their hand, has checked the address on it, and confirmed the issue date, the 14 day rule does not apply to any NIPs sent to their current address.