Women don't gain muscle like men do so don't worry about gaining too much of it. I think circuit training is a good idea but honestly just find something you enjoy and train with a bit of intensity. My girlfriend has lost 10 pounds in about 3 months of just exercising 3 nights a week with a good diet. Keep in mind she is Asian and only weighs 95 pounds(down from 105), so that's good for a girl as small as her.
I have her follow a very simple program like below:
Mon: Lower body 12-15 reps
Weds: Upper body 12-15 reps
Fri: Sports day, usually racketball for 1+ hour.
Then the next week she does 10-12 reps, next week 8-10 reps, repeat.
All she does is pick 4 compound movements on each day and do 4 sets in the specified rep range. I have taught her about positive failure and she seems to gauge the weights correctly when aiming for a certian number of reps. Every workout i make her choose 4 different exercises from the week before and each workout gets heavier every 3 week wave. It's pretty simple and anyone can follow the routine, there is no rocket science to any of this.
For you i would replace 1 hour of cardio with weights 4 days a week. If you are doing 2 hours of cardio a day you could lift for 1 hour first and then do an hour of cardio after you lift. Just keep it simple and don't burn yourself out in the first few weeks. Take your time and see what exercises you like and see what routines get the best results.
A few exercises i think women really need to focus on are: Overhead pressing, squats, lunges, goodmornings or SLDL, pull ups and bench dips.