If you have dumbbells, you have almost everything you need. I played football for many years and as a result my knees are tanked. Because I can't simply go out and run for cardio, I have had to use a weight training program to maintain muscle tone, while managing some cardio as well. If you circuit train very quickly you can get an excellent workout. Generally I take about 30 minutes for my entire routine, but I rarely stop for more than 10 seconds between sets, and I group my exercises. You need to establish a routine that works for you, but here is an examples.
With your dumbbells:
Concentration curls with your elbow inside your knee, then move to over head press grabbing the dumbbell with both hands. Rest, repeat (3 sets)
Shrugs, then move to calf raises. Rest, repeat (3 sets)
Squats toes in, then squats toes out Rest, Repeat (3 sets)
Crunches, then pushups Rest, repeat (3sets)
You just worked your chest, your biceps, your triceps, you back, your thighs, your calves, your core and your abs while getting a solid cardio workout as well. Add additional exercises as you are comfortable.
Don't worry, you won't bulk up, you will just start to see really nice definition, but I promise it will remain feminine. (Women always seem to worry about bulking up, so I thought I would add that caveat).
My 2 cents.