No. When would O'Brien have had time to travel to London with no one noticing that she was gone? O'Brien may delight in the misery of others, but she wouldn't murder someone just to mess with Bates.
When I mentioned upthread that Craig Ferguson had spoiled a major plot point on his show, it was Vera's death I was talking about. He talked about it when the season had just started airing here. He was speculating about who may or may not have killed her with his guest, who is a critic, and then (after some audience members groaned) looked sheepish and said "Whoops!" I was really glad I'd already watched the whole season or I'd have been really annoyed!
How many times can Sybil, feasibly, disappear out to the garage to talk to Branson? She's out there all the darned time and no one - except for Mary - seems to have noticed! She comes up with excuse after excuse to see him and yet still won't admit that she's in love with him. I've read interviews with the actors and they were frustrated too. With every new script and garage scene, they were practically shouting, "Just kiss already!" :lol
As a history geek, one of the things I love is how the characters are woven into major historical events. We get another one next week!