They didn't really frame her.. the world just conspired to make her appear as a villainess even if she never really did anything.
She wasn't even a fiance like most other of the same type of stories make the villainess to be, she's just a duke's daughter that was going out and about.
The damage, or harassment was most likely done by noble hearsay.
Clearly, the author never really tried to cover any plot hole and made it just convenient, it's kinda tiring to go into detail to everything just for more drama which the author probably didn't want and would rather a slice-of-life kinda thing.
Tho one thing for sure is the king didn't want this engagement since they even had to elope just to marry.