Bellatrix Lestrange is an evil character from the popular Harry Potter franchise, dedicated to the Dark Lord Voldemort, and played by the actress Helena Bonham Carter in the film version. She has long, dark, curly hair and a manic disposition that makes her a fun, if challenging, costuming choice.
Bellatrix Lestrange has long curly brown hair in the movie. Brown is a common hair colour, and the length can be fudged if the hair style isn't long or curly enough. Her hair is characteristically wild--as if she doesn't bother grooming herself often. This look can be achieved with backcombing your own hair or a wig. A cheap wig might be better, even, as it can simply be discarded (or saved for later use). Bellatrix has a light streak that is on the left side of her head, which can be achieved with a clip in hair extension--but many wigs come with streaks.
Bellatrix is primarily seen in two different outfits.When she is broken out of the wizard prison Azkaban, she is wearing a long, ragged, threadbare prison uniform. Later in the movie series she wears a black dress with a V-neck and sleeves that are laced on. The first should be easy to achieve- a long white nightgown that has had stripes done in fabric paint.
Clothes: Black Dress
A black V-neck dress with long sleeves would be the best place to start. Carefully remove the sleeves, and then sew the seams down. Then, using thick black thread or yarn, reattach the sleeve in a simple over-stitch. Leave at least an inch between the sleeve and the dress, to show the lacing. The sleeve on her costume also has some elaborate lacing on the underside, which can be achieved much the same way (split the sleeve up the seam and lace as if it were a shoe or a corset) but it only shows if she lifts her arms, so it's not absolutely necessary and can be skipped if time is a factor.
Clothes: Death Eater
Death Eaters, Lord Voldemort's elite group of wizards, have their own uniform. A white mask and a long black cloak that covers everything. It was originally designed around anonymity, so it covers everything. Most costume shops offer fully hooded cloaks, and patterns are available in most sewing stores for those who are inclined to sew. Bellatrix in the movie has a mask that's unique to her, but with a craft store mask, some paint, and some patience the same effect could be achieved.
Wand and Necklace
Bellatrix is often seen wearing a silver bird skull pendant in the movie. It's not necessary, but a silver pendant of some kind will help the costume feel more complete.
Her wand isn't particularly elaborate- it is a dark wooden wand with a bit of a curve to the handle. There are many places that sell wand replicas, but a stick that has been sanded and then stained with a dark wood stain would do just as well. A wand might be the most necessary accessory to all but the prison versions--they don't allow weapons in prison--so accessorise accordingly.
The character that doesn't have much to do with hair also doesn't have much to do with make-up, either, so not much is needed. However, using make-up to look like the character may help pull the costume together. Bellatrix was in a prison for years and is fairly pale, so it might help to lighten (using foundation or costume face paint). She has dark circles under her eyes, which can be achieved with non-waterproof eyeliner and judicious rubbing. Again, this is an optional step, so there's no need to go out of the way to worry about make-up.