During the loyalty mission you're told she's such a powerful biotic that she's nigh untouchable, hence the elaborate ruse to take her down. I totally bought into it, too, so I was disappointed as f*** when I managed to get her on my team and her biotics were no more powerful than say Jack or MyShep's. Oh well, lesbian psychic mind rape and asari in body suits are sufficient payoff for the mission.
...and somehow no matter how you customize her the Fem Shep is always so much better looking. Heck, to appreciate how much better looking Fem Shep is you don't even need to be physically attracted to that amazingly sculpted ass gyrating around in front of your 3rd-person camera for 100+ hours. It certainly helps, though :)