Neither of those. It means that they jumped in the ocean, but she (now) knows that this was a stupid decision. Jumping in the ocean is dangerous and stupid, and she's aware that they shouldn't have done this.
Here's a similar example. "I was crazy to turn down the job offer". This means that you refused that job offer. But you realise that turning down the job was an act of craziness on your part: you know that you should have accepted it. Only a crazy person would refuse such a good offer.