Bellatrix is the ultimate Pureblood: haughty, sadistic, power-hungry, and narrow minded. She's a complex character that plays that main role of being Voldemort's right-hand woman.
Here's a few question's about her:

Do you think she finds joy in torturing/killing others?
Do you think she's in love with Voldemort, or is it just the power?
Would she give her life for Voldemort, or is it more important?
Does she really love Rodolphus?
How deep do you think her feelings run?

These are just a few starters, I'm writing a fic centered around Bellatrix, and I need to know anything and everything about her!