Hi Christine,
Whichever option that you utilize - (he squat rack or plyo leg discs)(- it is very difficult for most women to "bulk up." Most women do no have enough testosterone to truly bulk up. In my opinion either option should accomplish your stated goal of leaning out and toning up your legs. Below is taken from Cathe's description of the two options
The Plyo-Workout is for those who don’t own a squat rack and will focus on explosive strength utilizing plyometric moves mixed with traditional leg strength training exercises. It will not follow the 5% method for strength.
If you wish to follow a true strength program and want to follow the same 5% Method used in the upper body workouts in this cycle, then select the Squat Rack workout option. There are two ways to do the workouts when selecting this option. The first and best way is to use a squat rack with safety catches and a spotter. Two members of the cast are shown doing this in all four squat rack workouts. The other way to do these routines is to wear a weighted vest (usually available at most stores from 10–40 pounds) and use a short and lighter barbell like we normally use in the other segments of STS. This still may not be enough weight for some people to exactly follow the 5% method, but nevertheless it will give you an outstanding and challenging workout. The purpose of the weighted vest is to lessen the amount of weight you need on your barbell. This is beneficial because in an exercise like a squat (without a rack) you are limited by the weight you can safely lift overhead, not by the amount you can squat.