Diana will always be aged up if something is happening sexually. Canonically, she's between the ages of 12 and 14, give or take a year or two. Rule of Rose is terribly ambiguous in that regard.
If you want to play with canon Diana (non-sexual), just be reminded that she is still an attractive girl for her age and she acts rather mature (in some ways more than others).
Likes:
- Easy to manipulate people
- Trolls
- Anyone who adores fairy tales
- Devotion
- Liars and cheats
- Weak willed people
- Strong men (who are devoted to her)
Dislikes:
- Strong men (who are not devoted to her)
- Physically abusive men
- Older women (think over thirty)
- The rich and snooty
- Physical touch that she does not initiate
- Being physically overpowered