Even diversity and technique would be subjective because people would value different aspects of each more or less.
If I was trying to do this I think I'd score out of 10 for each of:
1. Comeliness / Pulchritude (I just wanted to use these words for physical beauty lol)
2. Performance / Technique
3. Catalog / Longevity
4. Acting Ability
5. Range / Diversity
6. Aura / "It Factor" / Intangibles
[If I wanted to weight anything at all I'd probably do it from top to bottom highest to lowest]
I wouldn't shy away from subjectivity. Total up everyone's scores for nominated actresses and take median/mode values.
I'd piss people off with scores like Reiko Sawamura (4 for Looks), Hana Haruna (2 for Acting, 4 for Technique) and Hibiki Otsuki (9 for Technique, Range and Intangibles).
As you should.