In isolation, the words are pronounced identically. However, in context, there may be a liaison after the vous forms. Also, while not the case here, in classical singing (and occasionally in other types too), the e muet may be pronounced. For example, the listener in "Vainement ma bien-aimée" knows that Mylio is referring to a female beloved, not just ...
The two sound exactly the same.
Only the context can help to determine wich is wich.
Here it is clearly "libérée" because the girl is singing how she is liberated and freed from her past, and not giving commands to liberate someone (or herself).
At least it is how I understand it :D