Presea
Telly Talk Addict
I don't think the Wentworth fortune was just about the money for Katherine. She had a great concern for Wentworth Tool and Dye itself when Cliff started abusing it in season 5 (dvd). She also mentioned to Bobby during the barbecue about how she wanted to help Rebecca run the company. It was a family business and Katherine had an emotional attachment to it after growing up with her father. But it was ridiculous that Rebecca got away with this, because like you pretty much implied, I doubt that Herbert would have wanted any unknown children that weren't his getting anything like this, Rebecca's will or not. She didn't even stop to think about what he might have wanted.Katherine Wentworth going completely crazy came from two things:
1. For most of Katherine's life, she thought she was an only child, and that she would be the sole heir to the Wentworth fortune after her parents' deaths. Instead, Cliff and Pam get huge shares in Rebecca's estate after her death, yet Herbert Wentworth never found out about them before his death, even though he briefly met Pam and didn't know who she was. So the majority of Herbert Wentworth's fortune ended up going to the stepkids he never knew about.
2. Katherine was unable to seduce Bobby, let alone marry him. She was instrumental with subtle manipulation of turning Bobby and Pam's separation into a divorce in Season 7 DVD. When Bobby and Pam found out, they ostracized Katherine viciously. Katherine now used her hate from the estate dispute and her inability to get Bobby, by wanting Bobby and Pam dead, or to at least suffer for a long time.
Katherine's behaviour is wrong, but it's completely understandable. She felt that she was betrayed, along with the memory of her late father, and that Pam and Bobby still had the nerve to take the moral highground. It pushed Katherine over the edge.
Since Katherine did not try to do anything to get Bobby before Rebecca died, and and she even returned to New York until Rebecca died, then who is to say that Rebecca's death (on top of Katherine's father's death, too) had no impact whatsoever on Katherine's mental state. Before season 6 (dvd), Katherine had a career and a life in New York, and she displayed no hostility towards Pam during season 5 (dvd), and spent a lot of time off-screen and without Bobby It is not until Katherine returns in the next season that she throws everything away and is reduced to living in a hotel room while doing nothing with her life unless it is related to "getting Bobby". Based on my observations, I would say that it was almost like Katherine was using Bobby to fill the hole that came from her parents death. It might not have been as much of a romantic interest as she thought.

