Switch off location services on your phone when your getting close to the shop. And on a again as soon as your a safe distance or where you would be expected to be. Another option are signal blocking cases , that way you can’t be seen but you also haven’t switched off your location services (if she is really looking she could work that out)
Monger was originally a word which meant trade or barter. Thus an Ironmonger sold metal goods (hardware), a Costermonger, fruit and veggies, a Cheesemonger, cheese and a Fishmonger fish. However a Fishmonger's daughter was always (in Cockney language) a euphemism for a prostitute. Shakespeare used it in that sense.
Monger has always had a disreputable association, including in the modern usages Warmonger, Fearmonger or Whoremonger, so Fred F's usage is of ancient if not respectable lineage.