Hmm...what about Alberta/Gilberta/Norberta/Roberta/other names that can shortened to Berta/Bertie? I think Alberta is super-classy, and has a great meaning ('noble and intelligent'), and Albert is experiencing a revival so why shouldn't its feminine equivalent, but I'm not sure I'm brave enough to use something so unusual.
If you did use Beattie would you pronounce it 'bee-a-tee' or 'bee-tee' or 'beer-tee'?