This weakness is quite a drawback. First any weakness that reads "When you draw shuffle it back into your deck" is cause for immediate concern. The ability to draw any weakness more than once creates that much less of an opportunity for you to draw powerful player cards. The problem is magnified when playing an event heavy deck with many one shots that mush be continually drawn. I conclude that even if the card had no other text than what I quoted above the weakness would be still somewhat of a liability.
To add to my concerns, Stars of Hyades whittles away at Sefina's greatest strength (the events underneath her character card). But the greatest problem is that Sefina takes damage (and horror) when she can't remove an event underneath her character card and with Sefina only have five starting health I see a huge a liability.
How do you over come these? Having access to these cards seems like a good start: