[Urwen]

I can name a few women who were good rulers or otherwise instrumental for their fight against evil.

• Melian, the first woman-behind-the-throne. It was her power that protected her kingdom. It was her council that her husband listened to. Up until he didn't, which was when all the trouble actually started.

• Idril, whose premonitions were a key to the survival of the majority of her people. She and her husband constructed an escape tunnel right under the noses of both her father and the 'enemy within', so to speak, for months on end, without either of them finding out.

• Haleth is the epitome of this. She traveled through the lands where few dared to tread, and fought evil creatures of all kinds, from spiders to Orcs. She was also on semi-friendly terms with the son of the greatest Elf that ever lived, who granted her permission to dwell in the lands under his jurisdiction
• Eowyn qualifies too, I believe. She is of royal blood, and married a man of high political standing at that. She killed Sauron's chief lieutenant.