Hi,
Then I think that focusing on fat loss first may be best. Cardio is important, but diet is even more important. How long have you been going to Curves? Research has shown that the body adapts to the Curves workout very quickly and calorie burning is minimal...have you considered working with a trainer or someone to set up a program for you?
Once you lose fat you can work on muscle development without as much fear. DOn't worry, weights are not going to make you big. As a woman you don't have the hormones for it. But once you lose the fat a little muscle development will give you a firm, fit look.
Sarah