I'll ask one more time, since I got no traction last time. I'm not sure why I can't lie here. Does anyone know the reason? Maybe someone knows the variable name so that I can change it? What are the consequences of telling her the truth? Thanks.
I'm not 100% sure, but maybe the problem is you have not enough intimidation and/or charisma points.
You can edit your save file with
Ren'py Save Editor, obviously at your own risk.
Start the editor -> Click the Load Ren'py Save button -> Select your LISC save file -> Untick the Hide Ren'py Dialogs box -> in the quicksearch box type intimidation (yellow colored line with Integer type) -> In the Value column you can change the actual value to something bigger (try it with 20) -> in the quicksearch box type charisma (yellow colored line with Integer type) -> In the Value column you can change the actual value to something bigger (try it with 20) -> Click the Apply changes button -> Start LISC, and try out your edited save.
Note: Before all of that, create backup to your save files!!!