Recently, in certain segments of the modern orthodoxy there have been appointments of Yoetzet Halacha, a woman specially trained to assist woman with questions in Hilchos Neda. Is this permissible according to Halacha? Please give sources along with their reasoning. Please discuss possible issues according to the strict letter of the law and Hashkafa issues as well.
R Binyamin Tabadi (in the context of a question whether women can be poskei halacha) brings a few sources showing women have been ruling on halachic decisions in the past (in the sense of applying codified rulings, not creating new ones).
He quotes Sefer Hakhinukh (mitzva 152 towards the end) who writes
And the prevention of giving a ruling [by those who drunk alcohool] is [practiced] in every place and at all times by males, and so [too,] by a sage woman who is fit to give a ruling.
As well as the Chida in Birkei Yosef (CM 7:12)
... that even if a woman cannot be a judge, she can rule (lehorot).
And finally R Yissachar Tamar (the author of Alei Tamar, a commentary on the Talmud Yerushalmi)
There are many women in the history of the Jewish people who were "talmidot hakhamim". The sages and great men of Israel recognized their virtue and corresponded with them in words of Torah - and of course praised and respected them properly.
I have now also seen that the Pitchei Tshuva on SA CM 7:5 cites a number of authorities who rule that a woman who is an expert in halachic matters is permitted to paskin (decide) halachic questions (brought by R Howard Jachter here).
The gemara in Niddah 13b actually brings such a woman who used to tell other women whether the blood was tamei or tahor.
חרשת איהי תבדוק לנפשה דתניא אמר רבי חרשת היתה בשכונתינו לא דיה שבודקת לעצמה אלא שחברותיה רואות ומראות לה
The mishna states that competent women must assist a deaf woman. The Gemara asks: Let her examine herself; as it is taught in a baraita that Rabbi Yehuda HaNasi said: There was a deaf woman in our neighborhood who was so proficient in these matters that not only did she examine herself, but when her friends would see stains similar to blood and were unsure whether or not the stains were ritually impure, they would show her the stains.