Since we lack the details of the 'Mona Darling full story', it's difficult to define who Mona Darling is precisely. She might be a protagonist in a love story, facing challenges in her relationship. Or she could be a strong - willed character in a thriller, fighting against some sort of danger. There are countless possibilities depending on the nature of the story.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
Another theory is that it might be a composite of several different women. However, historical evidence mostly points towards Lisa Gherardini. She lived in the same time and place as Leonardo da Vinci, and the connection through her husband's commission is a significant factor.