I think just refusing to have sex with her also lowers dominance? I don't remember for sure but that can't have been the only way to do it.You have to specify what AT your Charlie is on before we can give help.
On Wednesday, Thursday, and Friday after bringing Diane back to her room, deny eating her out and go back to your room to watch Incest porn. Make sure she has high amount of Lust and you also have the topic Sexual Conquest in your hotbar before you watch porn. Two options should appear. The option you should choose is Really Give It To Her which requires the Sexual Conquest topic.
Also you can't give Diane the dress until she is on her Jilted AT.