the trick to losing weight is simple. burn more calories than you take in each day. understand just living burns calories, usually about 2000 a day (this depends on size and weight). check out
http://caloriesperhour.com. it has a calorie calculator, body mass calculator, tips on losing wieght, and is a pretty good site.
another benefit as a female lifting weights is it will increase your bone density and help with later osteoperosis, like sultana said. as stated, you will gain muscle, not bulk, and the muscle will burn calories while you sit there watching tv.
diet is very important. the healthier your diet, the more efficient your body will work and the harder it will work, resulting in better gains.