Rose was an ordinary Mage who swore her life to Lord Blackwell, but only for her and the Princess' survival—so she didn't expect that he'd suddenly go renouncing the gods.
And yet his words struck a chord within her and when she heard him speak? Despite all of the idiosyncrasies that he may or may not have had, there was something to be said when even the Vampire despised by the world started to make sense.
Rose didn't have an idea as to why Eleanor sent her here, but now she understood a little as she watched Cassius Blackwell paced about.
Now that he was no longer trying to portray himself as the ever infallible Vampire Lord, now that Rose could see a little more of his faults and issues that made her wonder if staying here was the right decision, she reached out and held his hand.
If Cassius Blackwell had grabbed her face when they first met, Rose would have bit off his thumb or sent a wind to blast him—but now she just held his hand.