Yes 3Ts should be in the clear. The wording is that the NIP must be posted so that in normal circumstances it will arrive within 14 days of the alleged offence (with the day following the alleged offence counting as day one).
However, 3Ts, there is one thing of which she should beware and it's quite important. Assuming you are the Registered Keeper the NIP will include a request for the driver's details. If you fail to respond to this, even though the NIP has been served out of time, you may be charged with an offence under S172 of the Road Traffic Act (failing to provide driver's details). The late NIP (especially one so blatently late as you describe) will certainly protect you against the speeding offence. However, it will not negate the possibility of a S172 offence.
You should complete and return the request for driver's details, decline the offer of either a fixed penalty or a speed awareness course and say you will be challenging the prosecution for speeding on the grounds that the NIP was served out of time.
This explains:
http://www.roadtrafficlaw.com/time-limit-for-a-s172-notice-or-nip