Its the giggling that annoys me more than anything. I like to hear laughter and giggling when its justified, but as you say, she giggles at the most inane things.
Plus, she is always interupting the other presenters, which makes it hard to hear what either of them are saying. Quite often she runs over the time limit, so she is cut off mid sentence when they go into the break - which smacks of incompetancy.