Unless you are taking steroids and working on lifting weights, there shouldn't be a worry about building muscle. Matter of fact, muscle is what burns more calories. I understand the fear of "looking like a body-builder" but theres not chance of that unless, like I said you are working out for hours in the gym daily and taking enhancement drugs. The average woman just doesn't build over sized muscle unless she's doing something beyond normal.
You want to tone and strength train not only your legs but your whole body to round out the body to look nice and firm. This burns the fat under the skin and makes for a nice healthy looking body.
If you are prone to more muscle on your legs then walking is going to help you get more elongated muscles than running and will still help you slim down. You want to walk fast enough to get your heart rate elevated a little but you won't have the joint impact that comes with running.
You can also do a lot of floor exercises at home to improve the tone and build muscle strength, not bulk you up. Diet will also help - lots of water, healthier food choice, don't eat late.
You want high reps low weight or resistance.
To build muscle men will normally do lows reps high weights so as long as you do the opposite and also remember to stretch a lot.
Check out my journal pages if you want some more ideas.