Erections during a dream are normal, but here we are talking about a dream of erection. Symbolically, this points either to fear of impotence or to the joy of masculine power. This symbol is about willpower and vitality within men and women. It almost always poses the question of how goal-oriented and focused your actions are.
For men as well as for women, this dream can be interpreted as the need for hetero-, auto-, or homosexuality.
According to Freud, women dreaming of erection indicates penis envy.... Little Giant Encyclopedia