I'm 22, 5'4 and I weigh roughly 109 pounds. I am trying to get down to 95-100 max, and I was wondering, in terms of making my thighs more slim, should I be running/walking on the treadmill more? I do own an elliptical and have been working out for almost 7 months more so on the treadmill, but I do work out of the elliptical sometimes no more than 35-45 minutes tops.
I tried increasing it though to burn more calories but I noticed that for the last 2 weeks that I go on it 4-5 times a week for nearly an hour and 10-15 minutes, I have been gaining what looks like more muscle in my thighs and legs. I don't want muscle, my goal is to just look more slim, not muscular. Treadmill or elliptical?

Thanks