Walk rapidly on a treadmill with perfect posture. It's the only exercise i know of that actually works to slim thighs.. the posture part is the key. I know it sounds odd but It's a modeling industry tick of trade. Otherwise, If you're looking to build muscle then you can do squats or leg lifts or something along those lines.
Sit on a chair (without the chair) with your back against the wall. This will build strength and endurance without the bulk of muscle. Do a minute at a time. As you progress, start to lift your legs. Don't overdo it, this can be painful, but it works!
walk up and down a hill or if you want to really work out your legs run up and down the hill with a back pack with 50pounds that would be good for your size 50 pound I use to play football and run up hills with a big back pack with 175 pounds in it gave me a nice butt too girl's tell me you have a.cute butt lol but try that