What actress played Mrs Lovett Bellatrix Lestrange Bucket and Corpse Bride?

You're thinking of Helena Bonham Carter.

She played:

* Mrs. Lovett in the movie adaptation of Sweeney Todd: The Demon Barber of Fleet Street.

* Bellatrix Lestrange in the Harry Potter films.

* Emily, the Corpse Bride in the Tim Burton animated movie "Corpse Bride".