I honestly don't know what to think about that page on Facebook. The Twiiter account that several sources have claimed is her real Twitter account (@Bella_Heathcote), normally tweets whenever the page is updated with a new photo or photos and provides links, and it has also done so in this case:
Bella_Heathcote Bella Heathcote
Johnny Depp as vampire Barnabas Collins on the 'Dark Shadows' set - pictures
http://fb.me/Cz9UIk7W3 minutes ago
But there's another account on Twitter (@BLHeathcote) that claims to be "The Official Twitter of Bella Heathcote". However, neither account has been verified by Twitter - and there are all sorts of other unverified Twitter accounts for all sorts of other celebrities that claim to be their official accounts but actually aren't - particularly in the cases where there are multiple accounts claiming to be the official one.
Obviously they all can't be.
So an unverified claim of being official is pretty much meaningless.
For what it's worth, @BLHeatcote has only one tweet:
BLHeathcote Bella Heathcote
This is *still* the *only* official Bella Heathcote twitter.
8 Jun
Whereas @Bella_Heathcote currently has 29. It's not like she's very active regardless of which one might really be her...
234 days 8 hours 41 minutes 32 seconds until the day the Depp/Burton Dark Shadows is released(ET)!!