1) Personality
This needs to numero uno in my opinion. I don't care how she looks, but if her personality is off, then it won't work.
2)Played by an Unknown
I don't just mean someone who has not had major roles in awhile, I mean an Unknown. I mean someone who may not even have an IMDB page right now. Someone who is waiting tables or still doing plays.
The reasons are:
a) A well-known would cause this to be marketed as "A Megan Fox movie" rather than about the IP.
b) Allows the Actress to give the role her best effort, and for both writers and actress to work to craft the best Honor we can get.
c) We would launch the career of a deserving actress.

d)Less costly.
3)Appearance
Mostly so that people can see the poster and they can go "Yeah that is Honor.". This will be the biggest challenge: "new film requires female actress for lead role. Must be Asian.6'2" or taller....".
If I had to do without 1 it would have be #3. Evergreen seems dedicated enough to get the Personality right, and having an Unknown would keep the actress from overshadowing the movie itself.