Unless you have no OH, family, friends or work colleagues, this is a scenario which could befall any punter. Being caught out somewhere where you shouldn't be is a constant hazard and, as in this case, usually very difficult to explain.
Yeah i've often been out on business in a company car or rental and "got lost" as i'm coming up the M6 finally ending up at a parlour in Manchester or Bury.
Often thought how I would explain being on the M62 heading in the wrong direction -
Got lost, don't think that would cut it.
Sat nav went nuts / programmed the wrong destination when I got back in the car after having stopped for a piss.
Got cut up by some twat who left the motorway too late and had to swerve to avoid being hit but it meant I also had to exit onto the other motorway, remember safety 1st
Have to say whenever I finally got back on the M6 I always gave a sigh of relief
In this instance the special gift or I was trying to arrange something nice for you / an event is probably the best tact as it will throw her off but you also need to be a bit dejected about it like "knew I shouldn't have bothered" as this may bring her on side and stop any questions / nagging