I couldn't say anything while 1795 was still going on, as anyone seeing it for the first time wouldn't know how Vicki managed to get back, etc. But, while she knew about Angelique being the witch and a lot of the things that went on, she clearly never learned about Barnabas. At first she thought he had gone to England, as she had originally learned, and then she was told that he was dead. She was in jail until the very end and never saw him again, so there was no way she could have learned the secret.
But, then what was it all about? It started with the seance and they tried to contact Sarah. When this happened, I assumed it was a means for her to learn the truth. But, while she learned about a lot of it, she never learned the real secret that was affecting them in the present. And, now she has partial amnesia and doesn't recall a lot of what she did know.
I can understand Barnabas being concerned about what she might know, but he should realize that she never learned about him. Of course, we're back to "dumb" Vicki. While she never learned that he was a vampire, she did learn that he died rather than going to England, so at some point she should start to wonder who this descendant is, but that part never seems to occur to her.
Meanwhile, just before the seance, they were all worried about David. One of his stories was about being hidden in the secret room, which everyone dismissed. When Ben took her to the secret room, how come it didn't suddenly dawn on her that this was what David had been talking about. And now, back in the present, she wants to check to see if there really IS a secret room, but she still doesn't seem to remember that David had claimed there was.