In the given temperature range she doesn't need an additional coat or anything. Her fur will be enough to keep her warm.
Her dog house should offer sufficient protection against bad weather. If she only has a cage or crate, you should cover at least 2 sides with thin wooden boards or other materials that stop cold winds. She needs a roof against rain.
What I'm most concerned about is the cold creeping up from the ground at night, when her body is still and doesn't produce much heat. In the long run that might cause joint pain and arthritis. You could put a thin insulation layer like straw or styrofoam beneath her carpet.
You can read her body language to gauge whether or not she feels cold. If she lies down curled up in the most compact ball possible, she feels cold and tries to preserve body heat. If you can see her belly when she lies down (on her side or in a curve), she feels comfortable. If she shivers she either feels cold or is excited.
To your second question: All Labradors have a summer and a winter coat, that is decided by their genes. You probably noticed her shedding massive amounts of hair some time in autumn. She got rid of her fine summer coat and started growing her thicker winter coat. You should brush her to aid the shedding and avoid matting of her fur. About 4 weeks later, when she stops shedding so much, her winter coat finished growing.
