The fact is whether you do high reps low weight or low reps heavy weight, your muscles will get toned. Heavy weight low reps will not necessarily bulk you up, and low weight high reps will definitely not get you cut (give you definition). A matter of fact, getting cut and being able to see definition has nothing to do with how you perform your lifts or how much weight you are using; it has to do with how much fat you have covering your muscles. Losing fat is the only way to get definition and to lose fat you must do some form of aerobics and you need to watch your diet. Most women do not have to worry about bulking up because no matter what they do, they do not have the quantities of hormones needed. Have you noticed how power lifters are smaller than most bodybuilders, and yet are much stronger? Power lifters work mostly with heavy weights low reps and although they do gain muscle, they don’t gain as much as bodybuilders.
So, to review, if you want to tone up, yes you do have to do some form of strength training, but you also have to do some form of aerobics and watch your diet so you can lose the fat that is covering your muscles and that will give you the definition you want.