In a one-on-one combat, I'm inclined to say a female lioness stands no chance unless it can get the tiger by surprise.
http://www.youtube.com/watch?v=D_PHs-kbypo
Wrong. A lioness (female) is trained from birth as a scrapper - trained to take down much larger prey. No matter what that prey is. And trained to take a helluva lot of punishment in the process.
A tiger is not.
Nor, strangely enough, is a lion.
A lioness is not the same as a lion. Lions have an entirely different role and different skill-set from a lioness.
A lion's job is to defend the pride against other lions and to intimidate rivals when it comes to mating. Beyond that, they spend most of their time being lazy, eating, and trying to copulate.
Further, a tiger may have size and bulk, but that is meaningless if you don't have the size and bulk
in the set of muscles where it needs to be. And what's more, a lioness will have more actual muscle mass than your average tiger.
Pound for pound, a lioness is the most effective combatant among the big cats.