I have a female client (around 30 years old) who wants to start bodybuilding. I did a bodybuilding-like program for her. She is getting good results and is happy with her upper body, but she thinks her buttocks have gotten too muscular and she can't fit into any of her clothes. What is the best way for her to "slim" down her lower body without losing muscles in her arms, etc? I recommended she perform higher reps and lower weights just for lower body.
We know females use the bio-mechanical advantage at the hips to squat, jump, etc, which utilizes the glutes a little more. So if we want to de-emphasize (for want of a better word) the glutes, we will need to encourage our clients to maintain a more upright position, which subsequently will emphasize the quads when squatting. This can be achieved by raising the heels off of the floor when squatting, which will allow the knees to travel forward a little more and therefore allow her to stay more upright.
Performing split squats will also allow your client to maintain a more upright position, especially if you raise the arms overhead, which again hits the quads and adds a nice abdominal element.
Note: Make sure you maintain her flexibility in her plantar flexors by doing some one-legged skirting board reaches to maintain strength in dorsi-flexion.
You can also mess around with the program design a little and perform some pre-exhaust (isolation followed immediately by compound exercise) on the quadriceps, so that they fatigue sooner than the glutes. This leaves the glutes comfortable in their ability to cope with the challenge and therefore not respond by growing.
So as an example: three sets of leg press - feet low on the plate to hit the quads. Leg extensions will hit the quads in a different active range of motion from squats (i.e., They hit the quads in full extension, and the squats hit the quads in flexion), so the quads can still be quite strong in the squat even if super-setted with leg extensions. Three sets of split squats? Three sets of squats, if needed? Maybe some dimensional lunges to maintain function at the end?
Good luck, and I hope this helps.