I was reading through this thread earlier and noticed that one of the posters experienced some problems while trying to upgrade from LHR (for his/her FRA-LAX - itinerary was LHR-FRA-LAX) due to contract agents.
My sister (2P) will be flying LHR-FRA-YVR in a couple of weeks and she has 1.5 hours layover in FRA - should she request for the upgrade at LHR or FRA? Thanks!