Very good deal. Why didn't you tell us it came with the internet cord? That just seals the deal.
(Sorry, couldn't resist!)
Like mcdermd said, the monitor alone is often valued at what you ended up paying.
My guess was close to her asking price! You could probably give it a better ad and flip it for double your money if you wanted to. Not saying that you should, just that you could. I used to do that years ago with local ads and surplus.