The issue is indeed complicated. There are those who say that women should not go up in order to avoid mistakes and there are others who encourage women to go up (Rav Yisrael Ariel).

A married woman may go up under the following conditions:

1) After the end of her niddah days and mikveh immersion, but before having relations. Some add a stringency of waiting an extra day, since we are concerned about her being a zavah gedolah.

2) A woman who has relations is considered "poletet shichvat zera" for 72 hours after relations (Shulchan Aruch Yoreh Deah 197:11). Therefore, a woman has to wait 3 days, go to the mikveh (without a bracha), and then she can go up to Har Habayit.

3) A kallah can go up before her chuppah, after going to the mikveh. There are those who say to wait an extra day because of zavah gedolah.

4) A woman who has recently given birth (yoledet) - after a week after the birth of a boy, or two weeks after the birth of a girl, if she stops bleeding, she can count 7 clean days, go to the mikveh, and go up to Har Habayit. Here too there are those who add an extra day. It is worth mentioning that there are those who say that a woman should do a bedika right before going up, just like a woman who eats terumah.

Regarding an unmarried woman:
Since chazal forbade single women to go to the mikva, there are those who forbid single women to go, so as not to violate this rule, and there are those who permit due to the importance of Har Habayit, and since chazal permitted single women to go to the mikva on Erev Yom Kippur.

Many issues regarding women going up to Har Habayit are still subject to debate. The issue can easily be avoided by having unmarried women and women who are in doubt regarding their status go up to the Herodian additions to Har HaBayit without entering the sanctified, halachic Har HaBayit defined by the Mishnah. This area is clearly defined and easy to avoid, with many visible landmarks to guide by.

B'ezrat Hashem we will be producing a map that clearly defines for all, men and women, which areas are not considered Har HaBayit and require no purification whatsoever. This route would need to be adhered to even more strictly than the route currently followed by most groups.

Again, it is important to emphasize that there would be no issue of karet or any other grievous sin involved in tresspassing the boundaries of halachic Har HaBayit without purification. One would simply not be following the Rambam's understanding of Morah Mikdash (Fear of the Sanctuary).

Yoel Keren