I don't watch 
Smallville, and I've haven't seen any of Laura Vandervoort's other performances credited at 
http://www.imdb.com/name/nm0888882/ . So I have no preconceptions concerning Laura's acting abilities, or on the wisdom of casting her on 
Smallville. 
However, perhaps Laura Vandervoort was somehow 
predestined  to play Supergirl... 
According to the IMDb site, she was born in Toronto, Canada on September 22, 1984. 
Toronto was also the birthplace of Joe Shuster, the co-creator of Superman. 
1984 was the year the Helen Slater 
Supergirl  movie was released. 
And take a look at the 
DC Universe Calendar and see who shares Laura's birthday -- September 22! 
http://www.geocities.com/the_time_trust_2000/calendar.htmSomewhat spooky, isn't it?