Light weight/high reps is going to create tight, lean muscles but not necessarily increased strength -- also good for endurance for athletes that require a slim/trim frame to perform... high weight/low reps is going to increase muscle size and strength... not always ideal for the average female. There should be a happy medium. You SHOULD break a sweat when you work out (especially an un-fit person) but then again you SHOULD be able to do reps.... I like 15x3 (15 reps, 3 sets).... 1 minute in between each, with the third being somewhat difficult. If it's not... increase weights, if she can't do all 3 sets... decrease weight.