"English speakers can use it in that way without any direct reference to the particular
Cassandra who lived in ancient
Troy"
That doesn't make sense to me, sorry. Without the mythological
Cassandra, there wouldn't
be a term such as "Cassandra-like", or the use of the name as a reference to prophetic behaviour.
The fact that the dictionary has included the reference to
Cassandra as a "definition" doesn't change the fact that this "definition" is actually a reference.
♦ Chrisell ♦
All we have to decide is what to do with the time that is given us. - J.R.R. Tolkien.