This is mostly a question based on the info we now know, the fact that she knew about the doings of the RAS the entire time and even asked them to do alot of it.
SPOILER FROM THE NEW BOOK
here is a summery of what happens in the book Arthas rise of the Lich King.
Sylvanas windrunner is alerted by a Doctor of the RAS that her experiments are starting to work and wants to show her the results (when she enters the RAS room it is full of hanging cages some human some forsaken) One test subject is a human female and one is a forsaken male who she is told is criminal but she thinks he is not she could care a less though. The doctor then gives the forsaken a cup to drink and forces the human to drink the cup when she starts to bubble and bleed through her eyes nose and mouth and then soon died, the forsaken took longer but soon he melted into a black pool on the floor.
she then tells him to take great care that this would be deadly in the wrong hands. The next part i am writing is right from the book and is one of her thoughts.
At last, Arthas, you will pay for what you have done. The humans who spawned such as you shall be slaughtered . Your scourge shall be stopped in their tracks you will no longer be able to hide behind your armies of mindless undead puppets. And we will grace you with the same mercy and compassion you showed us. Despite her great control, she found herself smiling.
Feel free if you voted before reading this to change your vote but do you think she cares for anything anymore or is she just evil and bound for revenge.