Are women obligated in Havdala?
Repeating Havdala for women: A person [whether man or woman] which has already said or heard Havdala may not repeat Havdala for women that did not yet hear Havdala unless there is a man or male child which is also fulfilling his obligation with this Havdala.
Hearing Havdala from a woman: A man is not to fulfill his obligation of Havdala from a woman. Although other women may fulfill their obligation through hearing another woman say Havdala.
Women are obligated in Havdala just like men. However men are not to fulfill their obligation through hearing Havdala from a woman. A man may not repeat Havdala for the sake of a woman to fulfill her obligation.
Are women to say the blessing of Meoreiy Haeish when they say Havdala?
Women are to say the blessing of Meorei Haeish when they say Havdala.
Are women to place their hands by the fire and look at their nails by the blessing of Meoreiy Haeish?
The custom is that women do not look at the nails.
May women drink from the wine of Havdala?
If a woman makes Havdala she must drink the wine. It is however accustomed for women not to drink from the leftover Havdala wine of someone else who made Havdala. The reason for this is because the tree of knowledge was a grape vine, and it is due to Chava eating from it that all women were punished to receive Nida blood. It is therefore improper for women to drink from this wine. This is in addition to the custom that no one drinks from the Havdala wine other than the person saying Havdala. The custom is to allow women to drink from the wine of Kiddush of which Havdala was said over on Motzei Shabbos that coincides with Yom Tov.
What is a woman to do if she cannot say Havdala over wine?
May male children be Yotzei Havdala from a woman?
In a time of need one may be lenient to allow children fulfill their obligation with hearing Havdala from a woman.
May women eat or drink prior to Havdala?
 A dispute in this matter is brought in Admur ibid.
First Opinion: Some Poskim [Rambam; Chinuch] rule Havdala is a Biblical obligation which is learned from the words Zechor…Lekadsho. They expound this verse to mean one must mention the Shabbos both by its entrance and by its leave. Accordingly also women are Biblically obligated in saying the words of Havdala just as women are Biblically obligated in Kiddush. This obligation of women towards positive commands of Shabbos is learned from the words Zachor Veshamor, which is expounded to mean that just like women are obligated in the negative commands of Shabbos so too they are obligated in the positive commands of Shabbos. The Sages therefore also obligated women to say Havdala in Shemoneh Esrei of Maariv and over wine just like the obligation of men, as in this regards both men and women are equally Biblically obligated.
Second Opinion: Others [Rabbeinu Tam; Shivlei Haleket; second opinion in Michaber] rule Havdala is only of Rabbinical origin, as the words Zachor only refers to remembering Shabbos when it enters and not when it leaves. According to their opinion some Poskim [Orchos Chaim; Taz] rule women are completely exempt from Havdala just as they are exempt from all Biblical and Rabbinical positive commands that are time dependent. Now although regarding the laws of Shabbos women are obligated in both Biblical and Rabbinical matters just like men, as since women are Biblically obligated in Shabbos the Sages likewise made them obligated in all the Rabbinical commands related to remembering or guarding Shabbos, nevertheless by Havdala women are exempt as Havdala is not a Mitzvah relating to guarding Shabbos but rather an independent matter which the Sages instituted that one separate between the holy and mundane. They supported their institution on a verse in the Torah which states “And to separate between the holy and the mundane”.
Third Opinion: Some [Maggid Mishneh; Meiri; Ritva; First opinion in Michaber] rule that even though Havdala is of Rabbinical origin, women are nevertheless obligated in Havdala. Their reason is because in their opinion Havdala is a Mitzvah relating to the remembrance of Shabbos and its holiness, as in it one mentions the difference between the holiness of Shabbos and the weekday. Therefore women are Rabbinically obligated in Havdala just as they are obligated in all matters which the Sages instituted due to the Holiness of Shabbos, as the Sages instituted that their Shabbos laws have the same status as the Biblical Shabbos laws. Thus just as women are Biblically obligated to remember and guard Shabbos as are men, they therefore are also obligated in all the Rabbinical enactments related to these laws.
The Final Ruling: The main ruling follows the latter [third] opinion although one is to also suspect for the second opinion. Hence one [whether a man or woman] who has already heard Havdala is not to say Havdala for only woman, as according to the second opinion women are not obligated in Havdala and one is hence saying a blessing in vain. Nevertheless the women themselves may say Havdala even according to the second opinion which holds they are not obligated to do so, as a woman may choose to perform with a blessing all positive commands that they are exempt from. [ibid]
 This ruling of Admur ibid follows the ruling of the Bach brought in M”A 296/11; So rules also: M”B 296/35; Peri Chadash; Ashel Avraham Butchach; Siddur Yaavetz; Kitzur SH”A 96/3; Aruch Hashulchan 296/5
Other Opinions: The Rama [296/8] rules women may not say Havdala themselves, and are rather to hear someone else say it. So rules also Taz 396/7 and Kaf Hachaim 296/58; Divrei Yatziv 1/135
Custom of Sefardim: Yabi Omer 4/23 rules that according to Michaber women may say Havdala themselves.
 See previous footnotes for the reason.
Other Opinions: The Zechor Liavraham and Bircheiy Yosef [brought in M”B 296/36] rule that a man may repeat Havdala for a woman. So rules also Ben Ish Chaiy Vayeitzei 22; Aruch Hashulchan 196/5; Oar Letziyon 2/22-3; Yabia Omer 4/24; Tzitz Eliezer 14/44
 In order to suspect for the second opinion which exempt women from Havdala [ibid] as well as due to that they should not come to belittle Mitzvos. [271/6]
 Ketzos Hashulchan 96 footnote 12; So rules also Daas Torah 296; Ben Ish Chaiy Vayeitzei 24; Kaf Hachaim 296/54; Igros Moshe 2/47; Kinyan Torah 1/88; Beir Moshe 4/28; Kaneh Bosem 3/17; Sheivet Haleivi 6/42; Yechaveh Daas 4/27
 So is proven from Admur which does not mention anywhere any differentiation regarding women in the blessing of Meoreiy Haeish. Furthermore, even according to those Poskim [M”B in Biur Halacha 296 “Lo Yavdilu Leatzman”] which side women are exempt from the blessing of fire, they are nevertheless permitted to say the blessing as is the law by all Mitzvos that they are exempt from. [Ketzos Hashulchan 96 footnote 12]
 Ketzos Hashulchan 96 footnote 12
 The Ketzos Hashulchan ibid suggests the reason for this is because before the sin of the tree of knowledge Adam was clothed in nails, and the sin which was caused by Chava caused him to lose these nails and have them remain only on the fingers, therefore they do not look at them.
 M”A 296/4 in name of Shlah
 Shlah ibid
 Perhaps this is the reason Admur omitted this custom although it is brought in the Magen Avraham, as it is included within the custom that no one, not even men drink from the Havdala wine.
 SSH”K 62/16
 See Halacha 7
 See Halacha 14
 Piskeiy Teshuvos 296/20
 As they are obligated in Havdala.