What is a mohel/mohelet?
A mohel (or mohelet for women) is a shaliach--or agent--for the father, who was traditionally the one required to perform the bris. Over the years, families designated a mohel, one who is trained in the rituals and procedures of the bris, to actually circumcise the infant.
In modern times, more women have become mohels. The actual term is mohelet. In the Torah, there are only two places where the performance of the circumcision is mentioned. One was when Abraham fulfilled the covenant with G-d and the other describes Zipporah, who was Moses wife. She stepped in and circumcised their son herself. There is no place in the Torah that states women cannot perform this covenant. The fact that until recently men have only been mohalim is only minhag, or tradition--there is no basis in halacha (Jewish law) that states it is not okay for a woman to be the mohel(et).