I have a theory in mind.
Vena is aware of Baiser's betrayal or is realizing it now.
The bases on which I am basing myself are the following:
1: Baiser's attitude in this chapter should raise your attention, she before becoming a berserker was antagonistic against vena but now she acts in a respectful and friendly way with him, add that due to how focused he was on his plans that a third party was able to ruin them and that baiser suffered a change in form I can make vena begin to suspect or outright realize utena's intentions
2: the fact will reveal that Baiser is about to verita is confusing, it is established that vena's plan is to make baiser go crazy, absorb a group of magical girls and consume her afterwards, vena should be against that for truth means dominance over one's mind unless disclosure is part of their plans
I imagine that what will happen is that when Baiser reveals his plan and executes it, it is revealed that he had already foreseen it and was "Out-Gambitted" for a moment and possibly seeing his plan fail leads Baiser to a mind-break moment the which vein will he take advantage of to take her to her berserker state.