How do I defeat the broodmother on dragon age origins?

I cant get past this stupid creature and its beginning to get on my nerves. I got her life down all the way to the point where if all my party members attack at once, i could kill her; However The dark spawn and her tentacles take us out every time. I play as a human noble and my party members are Zevran the elf, Wynn the circle mage, and Morrigan "the witch of the wilds". I also have At least 15 potions. But i still need help. ( it's the ps3 version, if that's any help)