She will fill Bellatrix Lestrange's shoes
This is a great casting choice:
Helena Bonham Carter, an Oscar nominee for The Wings of the Dove, who most recently starred in the hit film Charlie and the Chocolate Factory, has joined the all-star cast of Harry Potter and the Order of the Phoenix. Bonham Carter will play Bellatrix Lestrange, Sirius Black's cousin and a Death Eater, who is one of Lord Voldemort's followers (WB Press Release).
She looks like Lestrange, and will be able to pull off the role. I can't wait to see this film.