Note: you should post such questions about the legacy games in the forum Prince of Persia Legacy
That is where you will find the answer below as well as answers to future questions about that game.
Location: Fighting the Woman in Black at the Sacrificial Altar
In order to fight "the woman in black" Shahdee at the Sacrificial Altar, use the same technique you used earlier to defeat her on board the ship.
Yes, it is tedious. Yes, even on the "Easy" setting it is challenging if not too difficult.
Keep Shahdee away from the woman in red.
Attack Shahdee and lure Shahdee away from the woman in red.
You can not just slash and slash at her relentlessly. Maneuver around her to attack her on her side.
Then attack her from the front or rear. Keep moving.
(I usually got skewered by trying to vault over her, so I usually avoid that strategy.)
You should learn how to roll away from her either to the left, right, or backwards with backflips.
Learn how to use a wall vault attack to injure her.
You must be "sword-to-sword" fighting Shahdee at her 75%, her 50%, and her 25% health levels in order for some cinematic scenes to display.
If she kicks you into the chasm or severely injures you in a short period of time, use the Power of Recall to rewind time to when you were healthier.
If you selected "Hard" difficulty and can not defeat her, you may want to start a new profile selecting the "Easy" difficulty setting.
1] Slow way. Keep staying away from her and that means roll or flip away after attacking her. Keep luring her. When she gets disinterested and goes back to attack Kaileena, back attack her and run away again. If you climb up the stairs halfway towards the exit or a couple of stairs below from where you entered the arena, she won't follow you. After playing her attack moves in air she will back away to attack Kaileena again so you can go back to attack her from behind again. Blocking her in a straight fight is no good as it is tiring to wait to attack and she will eventually get through and kick you hard enough or get a few attacks in to do damage. All these delaying tactics achieve is frustrate you. But if you have patience and less skills to play, they will work slow and steady.
2] The best way to beat her is to run away by rolling, dodging or flipping out of her way after attacking her, then running upto her to vault attack her [The moment you are close enough to her after running towards her, press forward key and jump key once to jump over her. Attack her while in air and after you land behind her.] You can get 2 to 3 slashes in her easily than flip away from her [side or back buttons with jump key]. Run to her again and vault attack again and so on]. You could play a few practice sessions with her here even if it means dying just to get a hang of this tactic. Once you get a hang of it she will die in 2-3 minutes flat and you will enjoy it the most. This moves you must practice and master [vault attack and flipping away after attack] as it is most helpful in beating the Empress of Time later in the game.
One more thing - The secondary weapon does a lot of damage so do hit her with a couple of combo slashes after vaulting wherever possible and then back flip away. Vault attack isn't tough. I died like 25 times in frustration here before I saw videos on youtube and saw how vault attack changed the fight. I got that rythmn within a couple of rematches and successfully killed the ***** without getting screwed again. It isn't difficult at all. Just train yourself against her a few sessions in the same arena without getting butchered bothering you. In case your secondary weapon breaks after a cutscene or 2, break the rack on left side of exit stairs and get one. The whole fight is easy. Only place you need to watch is cutscenes at 25%, 50% and 75% of Shahdee's health. You have to keep and pressing attack and when the scene is over flip out of the way. It is here she can damage you a lot if you don't attack fast or break away fast.