I haven’t ordered one myself, but I’ve just visited the Peugeot Motability website and it reads quite clearly to me.
Navigation is being offered as a no cost extra on the AP on all 2008 Allure models.
Don’t let the dealer fob you off. Challenge him and tell him that you want navigation added to your wife’s order as per the Peugeot website.
If necessary, cancel the order and go to another Peugeot dealer who will honour the deal.