All perfect praise be to Allah the Lord of The Worlds. May His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
It is permissible that a female non-Muslim doctor treats a female Muslim patient. Rather, this is better than her being treated by a male Muslim doctor. In terms of fascination, her being treated by a female non-Muslim doctor is of lesser harm. Al-Shirbini (May Allah have mercy on him) says: "When a woman is in need for treatment and there was a female non-Muslim doctor and a male Muslim doctor, then it is better that the female non-Muslim doctor treats her. This is according to the apparent opinion of the Shafie Madhab, as stated Al-Azru`ei, because this is of lesser harm in terms of fascination. This is in addition to the fact that the female doctor only looks at the female patient`s body as much as needed for delivering proper treatment." {Moghni al-Mohtajj, vol.4/ppp215}. And Almighty Knows best.