After watching this video by Pyromancer, I think I've finally realized her true intention. Listen to the few things he says before the reaction video.
She didn't go to ICC to hurt Bolvar. If that was her intent, she wouldn't have left him alive. First, she released him from his own prison with the helm. Then she shatters the veil between Azeroth and the Shadowlands.
I'm pretty sure that shadowy figure she's standing in front of is chained down. She's using him, for the greater good, or waiting for us to follow to help bring this guy down. This shadowy figure is disrupting the balance, or is keeping this 'prison' in check for the Titans.
The titans will witness these efforts Sylvanas is going through, and will try to stop her, but in the end, I believe she's going after the titans.
"And I will set us all free." - Sylvanas