Eustacia is, quite simply, a narcissist. That was not how people were defined at that time. She may have been seen as self centered, heartless, hedonistic - all primary traits of the narcissist.
A previous reviewer was confused by the use of of the adjective, "Titanic" and the emphasis Hardy attached to it. The definition, "of exceptional strength, size, or power", is both descriptive and emotive and gives the reader a sense of place and the importance of the heath in it's formation of and importance to, all of the characters.