No, it is very difficuilt for a woman to build muscle. For a woman to gain muscle she would need to be lifting the maximum weights she could lift for 6 to 8 repititions and eating a very high calorie high protein diet.

If you feel yourself that you are getting muscular, this is just muscle tone, where the body stores water in the muscle cell in the form of glycogen making the muslce feel more firmer, this is fine, required by the body and healthy.