Should she seek help in taking care of her skin from a female Christian specialist?
Question

What is the ruling on going to a skin specialist, who does everything that women need for their personal care, but she is a Christian? I would like to point out that I have been going to her regularly for three years, only once every month, to take care of my skin, and I am afraid to go to anyone else. I should add that she has a very good attitude, but after I became religiously committed I started to worry about going to her before finding out the ruling on that.
I am afraid to go to anyone else because most of those who work in this field are Christian woman and the Muslim women I know who work in this field do not have much experience.
Praise be to Allah.Firstly: 
It is not permissible for a woman to let anyone see the most private part of her ‘awrah, whether that person is a man or woman, a Muslim or a kaafir, apart from what happens between the spouses. And there is no exception from that except what is needed of looking for the purpose of medical treatment. 
See the answer to question no. 5693 .  
Based on that, if this skin care requires uncovering the most private part of the woman’s ‘awrah, she has to take care of it herself and not let anyone see it, even if that is a Muslim woman, let alone a kaafir woman. 
See the answer to question no. 97938 
Secondly: 
If a woman needs to uncover the most private part of her ‘awrah, as in the case of giving birth, then the basic principle is that a Muslim woman should take care of that, and she should not allow any non-mahram man or non-Muslim female to see it, if there is a Muslim woman who can take care of that. 
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: 
The words “… [or] their female associates…” [an-Noor 24:31] are a precaution against mushrik women, so a mushrik woman should not be a midwife for a Muslim woman, and she should not enter the hammam (bathhouse) with them. But Jewish women used to enter upon ‘Aa’ishah and others and see their faces and hands, unlike men. So that is part of the visible adornment with regard to women of ahl adh-dhimmah, but dhimmi women are not allowed to see the hidden beauty and adornment.  
Majmoo‘ al-Fataawa, 22/112 
Thirdly: 
If she cannot find a Muslim woman to treat her or her problem requires uncovering her ‘awrah or part of her hidden adornment, and the one who is going to do that will either be a kaafir woman or a Muslim man, then it is better to let the kaafir woman do it, because in that case the risk of fitnah is less, and because she is of the same gender, so it is also less likely that there would be any looking or touching with desire. 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 
It is preferable for a trustworthy Christian female doctor to treat a woman rather than a Muslim man, because she is of the same gender, unlike the man. 
Fataawa Ibn ‘Uthaymeen, 12/218 
Fourthly: 
If the matter does not require uncovering the most private part of the ‘awrah or the hidden adornment, it is permissible for a woman to seek the help of a Muslim woman with regard to some of her needs that have to do with her personal care. 
See the answer to question no. 97938 
Is it permissible to seek the help of a kaafir woman in this case, as mentioned in the question? 
That is based on [?] the difference in scholarly opinions concerning the ‘awrah of a Muslim woman in front of a kaafir woman: is it the same as her ‘awrah in front of a man or is it like her ‘awrah in front of a Muslim woman? 
More than one of the scholars favoured the second opinion, that there is no difference with regard to looking between a Muslim woman and a kaafir woman, if she is trustworthy with regard to such matters. 
It says in Fataawa al-Lajnah ad-Daa’imah: 
Is it obligatory to observe hijab in front of a kaafir woman or may one interact with her in the same way as one interacts with a Muslim woman? 
There are two scholarly opinions concerning this matter, the more correct of which is that it is not obligatory, because that was not narrated from the wives of the Prophet (blessings and peace of Allah be upon him) or from any of the female Sahaabah when they met with Jewish women in Madinah and idolatrous women. If that had happened, it would have been transmitted to us as things that are less important were transmitted. End quote. 
Fataawa al-Lajnah, 17/287 
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 
The ‘awrah of a woman in front of another woman is the same as the ‘awrah of a man in front of another man, whether she is a family member or an outsider, a believer or a kaafir – there is no difference. 
End quote from al-Baab al-Maftooh, 85/13 
See also the answer to question no. 82994, 2198, 6596, 21953 
Based on that, if you need the help of a trustworthy Christian woman in taking care of your skin, that is permissible if it does not involve the most private part of the ‘awrah. However seeking the help of a Muslim woman for that is preferable, because of the strong difference of scholarly opinion concerning the matter and because many of the scholars did not allow such things. Rather the basic principle is that a woman should take care of that herself so long as it is possible, and she should not go to extremes in such matters as some women do who have nothing else to do. 
And Allah knows best.