I said just a few weeks back that Cassandra made a mistake not to at least try to get on the good side of Elizabeth.
Probably true - it would have been good strategy. But given Cassandralique's temper, and given the remark Liz made to her on the very first night she arrived at Collinwood:
[spoiler]
1968: Ep #474 - Liz believes Cassandra could make Roger happy
by annulling her marriage. ( You've just got to love the way Liz
'welcomes' her new sister-in-law! ;-) ) [/spoiler]
I suspect Liz very quickly went to the top of Cassandralique's Must-get-revenge-against list. And given how twisted she also is, it probably gave her immense pleasure to cause Liz to only think of death rather than to make nicey-nice with her.
One of Angelique's biggest problems has and probably always will be that she doesn't think things completely through before she acts. But then, what fun for the audience would it be if she did and we didn't get to see how things often come crashing down around her?