Veronica woke up with that revelation all thanks to her spirits and knowledge in witchcraft. Now, that she knew who wrote the note, the name of the person, with some spells done on the piece of note she found in Damon's safe and putting it under her pillow to sleep on it, she was able to see all the history of the person that wrote the note and deduct the truth.
The witch rose from her bed and went straight to her vanity table in disgust. She'd always known Damon had more up his sleeves and a big fraud. The whole show of being the best brother in the world to Rayven, even though she was not entirely a saint herself, but she was against monsters that hurt or endanger women. Demon or human she frowned against them like they were shit.