Archnemesis, @, is the Warrior quest nemesis. She is extremely difficult: hits hard and often, steals your items to teleport away with them, seduces you to steal multiple items in a single turn, and ignores Elbereth.
Archnemesis is incredibly ferocious in a straight-up fight. Fortunately, she has weaknesses, and a wise Warrior will exploit them – in the words of Sun Tsu, "You may advance and be absolutely irresistible, if you make for the enemy's weak points." Archnemesis's weaknesses include her predictable behavior (teleporting to the upstair to heal), and her lack of key resistances (sleep, level drain, and poison). Your strategies should generally strive to play upon these weaknesses.
Even with a good game plan, you may find Archnemesis a deadly opponent. You will want a very low AC to degrade her attacks (-20 is comfortable; you may get by with less), enough HP to survive multiple rounds of combat against her (200+), and a very high Luck to ensure that you are able to hit her. Being female makes you less susceptible to the multiple item-stealing attacks (consider using an amulet of change). All of this – and the strength of the other enemies you face on the Quest – indicates postponing this battle until you have had enough time to prepare for it. Generally, you will be strong enough after you have finished the Castle and retrieved the luckstone from Mine's End.
Paralysis or sleep
Wield or throw a potion of paralysis while wearing a ring of free action or zap her with the sleep spell or wand. Make sure you can use this method multiple times to ensure her immobility – you may miss, or she may wake up before you finish killing her.
Sleep is a keyword to defeat her even at level 14 – it is difficult to overstate the power of this lowly spell against Archnemesis. After rendering her helpless, be sure to hit her hard. Mjollnir is an excellent choice if you have it. But one or two of the stronger attack wands, such as Lightning, Fire or Cold will work nicely as well. About 12 shots total should suffice, again assuming your luck is sufficiently high and you don't have too many misses.
Use the drain life spell until she croaks. It is a good idea to do this on the level above and when she teleports away (to heal the modest HP damage that drain life does on top of the draining effect), go downstairs to heal yourself, preferably on a burned Elbereth.
Fight Archnemesis mano-a-mano. Not recommended. Archnemesis has a higher base damage than any other monster, resulting in very stable and impressive damage, and her item-stealing attacks will strip you of the weapons and armor you need to stand up to her. You are therefore opposing her strengths with your weaknesses. If you decide to go this route, make sure you are female (use an amulet of change if you are not), have high health, low AC, and if at all possible, half physical damage.
You may want to use the potion of invulnerability to make this fight easier. Remember, you still need to have a strong offense so you can take out Archnemesis before your invulnerability runs out.