Beelithina wasn't aware of Vlad's existence because he had little to no aura, she assumed she was the first to convert a human but that wasn't the case even though Lucifer had created a flawed creature.
Vlad was defective, he needed to consume human blood to survive and he had already given his soul to Lucifer to consume.
There was no soul within him, he was an empty carcass that had lost the very thing that made it an entity and this was why Lucifer was fascinated by Kenzo.
Beelithina knew that she had to do something about this, she didn't know what was coming but they had a lot less time for that to happen.
Lucifer shouldn't have been able to possess someone unless he had help from someone here in the human world who lifted the veil to the demon world.
She recalled her day with Kenzo and got goosebumps just thinking about it.
She was a Succubus and no stranger to sex yet Kenzo had managed to dominate her in ways no one ever could.