One question: is it necessary for a beginner to do long hill climbs? I think not. Well, not that soon. Building aerobic capacity takes time depending on age, the number of times a week a rider goes, etc.
Hill climbing shouldn't be avoided, but is not necessary for the beginner. I would let the beginner gain confidence first. Confidence in the ability to ride for an hour without being concerned that he/she cannot finish. Confidence that there is a sweet spot in the pace and even improvement in pace.
Its a lot like distance running.