It's to prevent unlimited grinding while making it easier to get to a boss if you're having trouble in a level.
Well, that honestly depends on your build. Many of the tips are general and go for many of the bosses in the game. As a melee character, you can tank up with a heavy shield, good stamina and a lot of poise, sticking close to her and circling around to counter after blocking her combos, or go light on the equipment and roll out of her way, again circling around and trying to get one or two hits in (never deplete your stamina completely, it makes you far too vulnerable). For external help, there's a way to light up the arena you're fighting in, and you can summon an NPC called Lucatiel for that fight to share aggro, which will give you more windows for healing, attacking etc.
Good luck!