Gut her health regen and give her Q a shield scaling for 100% of her AD whenever she tumbles. This will force Vayne players to rely on the shield to block harass in lane and actually gives her a weak laning phase while not hitting her mediocre late game too hard.
I see what you did there.
sounds more like a buff to me...
Drag her champion files from the servers to recycling bin. Empty the recycling bin and proceed to burn down everything that has to do with her.
Give her silver bolts proc a cooldown. There's a better solution... The shield will make her more obnoxious than she already is
