Lambda's ability expires inmediately because it only works once, and it's at the exact moment it is activated, to deplete the Guard Break guard. However, that doesn't mean the partner's ability expires at the same time, both work separately.
And this is why I love her Dive kick. Never seen one that allows that much comboability. It's the second hit of that combo.
http://www.youtube.com/watch?v=MOFqeUUf9oo