What makes Ezmerelda so good that she is so expensive on ebay?

I must be missing something. Aside from rarity what is it that makes Exmerelda so darn good that she costs $50+ on ebay? I mean, is she the new hot tech for the Girls decks or what?

Only rarity.
The 4 rare vampires from that set started out at ~$20 and have only gone up since then.

Thanks for the info. I was thinking I might have been missing some huge obvious thing. I wonder what cards will be going up in price in the near future in addition to Enkil Cog and older rare cards like Ezmerelda.