Your interpretation would make Lilian awfully simplistic, and I prefer to believe there's a pathos to her actions: and her
appearance in the Scarlet halls support this. Even though revenge is one of the motivations, she clearly states that she sees the Crusade has becoming irredeemable evil and in need to be destroyed. To this end, she seeks the aid of adventurers.
Now, you are free to believe that she is lying about that.
The "freedom" thing was mentioned with quotes the first time for a reason. It was not something done in purpose, but none the less it opened the floodgates. Lilian was THE person to destroy the Crusade from the inside, and no one knew it. It wasn't fate, it wasn't coincidence. Had Lilian died to never be raised, nothing would had happened. But she was, and this gave her a second chance, to see the sins and lies of the Crusade. Their scorn fueled her anger and desire for revenge and this lead to their definitive -probably- end.
So yeah, she does "owe" them, even when it was not their intention. I think she can appreciate more the random nature of the causality of this path, instead of it being born out of machination. Had the forsaken "used" her with intention, bet your sweet ass they could be primary targets on her list. You have to see that undead meant more than just reanimation for Lilian, it was the first times she was truly free of will, not controlled, ordered or manipulated for anyone.
She was finally free, and the forsaken -and Sylvanas- where the responsible of this. As such, I believe there's an small appreciation shown in the form of keeping out of their way; for the time being, at least.