This article cites varying opinions regarding the use a mohelet - woman circumciser. There are opinions allowing it, though.
There is a controversy in tractate Avodah Zarah 27a regarding this very issue between Daru bar Papa who cites in the name of Rav and Rabbi Yochanan. Here is the substance of the argument. Daru b. Papa held that only someone who is obligated to observe the precept of circumcision can act as Mohel for others, whereas R. Yochanan felt that a woman can act as a Mohelet as indicated in the story of Tziporah (see Exodus 4:24‑26 for details). You could say she was a Moyhel of a goy’ol (pardon the pun!)...
In practical terms, R. Yosef Caro, the Halacha follows R. Yochanan and a woman may act as Mohelet (Yoreh Deah 264:1) but Maimonides adds one stipulation: this only applies in the event that a male Mohel is not available (MT, Hilchot Milah 2:1). However, Rema cites authorities who differ on this matter
The article author cites a theory which, to me, seems speculative. Is there any reason emanating from Responsa or some Rabbinical decision or custom that discourages or prevents the use of mohalot? It seems that their use is rare in Orthodox circumcision but somewhat common in Reform circumcisions.